Garmin connect only synced most recent 30-day data to apple health

That's normal.  If you grab RunGap from the App Store, it has the ability to do what you want if you are referring to workouts/activities (I don't know of anything that will pull metrics from Garmin to HealthKit outside of a recorded activity).  Normally it's a paid feature but the developer has made it free for the rest of the month.   I have no idea how well Garmin plays in the Android space, but do be ready to find that their integration with Apple Health is sorely lacking with a lot of outstanding issues that have existed for years and in the opinion of some folks on this forum makes it pretty worthless.  

Thanks for your reply. Workouts/Activities aren't that import to me. I am more interested in Resting Heart Rate, Steps, Hear Rate, Sleep, ... as I really like the visualization and trend overviews in Apple Health. With only 1 month of data, there's hardly enough data to show any trend 

Heart rate and steps should work fine. (you will actually get more heart rate samples from connect than you would wearing an apple watch).  Steps will be done in 15 minute intervals, which isn't ideal, but probably works well enough for most.   Sleep is going to give you time in bed, and time asleep, but wont' give you sleep phase (which some people consider a guess anyway).  Resting heart rate will give you a single value at midnight I believe, which should be fine, but be aware that I'm pretty sure Garmin and Apple don't use the same logic to determine it).  

Alright thanks. So there's no app/way to export/sync my last two years of historical data to Apple Health? RunGap only exports activity data

Hi! I’m an aspiring Garmin owner: I’m considering switching from AppleWatch to Garmin (or at least use both depending on circumstances). I too would like all of my health data to still be in the Apple Health app though.

For all-day heart rate data, how many data points are synced from Garmin to Apple Health? I mean what values are exported? All readings (every second I guess?)? 2-min averages? Thanks! :) 

You should expect to get a HR value every two minute (no clue if it's snapshot or average).  For activities you should expect to get summary metrics (e.g. a run will give you start and stop times, total distance, and total calories burned, each as a summary only)

Hi Wizard, question about steps, if I turn on steps from connect to Apple health will that duplicate my steps if I use both AW and a Garmin at times ? Or is health smart enough to estimate the combined steps? Or should I leave connect steps off ? Right now I have everything turned on to health except flights climb and steps .. hope this makes sense ..

Keep in mind that I'm out of date since I gave up on Garmin doing a proper implementation of HealthKit months ago.  That said, when I last checked, Garmin correctly wrote steps info HealthKit in 15 minutes blocks.  So, depending on if you have your Apple Watch or your Garmin at a higher priority in Health, Health will do just fine in combining both.  BUT, keep in mind that the 15 minute blocks mean that if you have Garmin at a higher priority and with take one step at the start of a block and then switch to your Apple Watch and do 500 steps in then next 10 minutes I don't think they will show up.  (Health will see that Garmin said "1 step" for that window, and Apple Watch says 500 steps across a bunch of smaller blocks within that same window and ignore the Apple Watch.   Likewise, I suspect *but never tested) that if you reverse this scenario then Health will ignore the Garmin values because you have Apple Watch data for that block and it's the higher priority.  SO, you shouldn't really get duplicates, but you will potentially get an undercount.  It shouldn't be too major unless you switch back and forth a lot (or at a really bad time).  They may have changed it, but when I last check Flights climbed was unusable.  Garmin would record it several times during a day, each time being the current total, and using a time stamp rather than a range.  So they were creating duplicate data even before you add an Apple Watch to the mix (and saying you climbed 20 stories instantly, but thats a separate issue.).  In the end (and at the time) Heart rate and steps werethe only all day metrics that you could let Garmin write to Health without causing issues.  (in fact, Garmin did a much better job of writing heart rate to Health than Apple does.). Hope this helps.

Thanks so much for the response, this helps alot…I think I may just stick with using rungap .I use both Apple Watch for daily wear and strength workouts and Garmin for cycling and runs and never found a a good way to keep everything in on place ….. if Garmin would just write properly to HealthKit that would be great 

Yes RunGap is great  I use it to send to Strava and Apple health. Nice as one can edit the activity (notes etc) in GC in your own time then send to the other apps when ready. Also great for sorting out history loading!