Any way of tuning race predictor?

I really don't understand your antagonism. Yes, every time I run a TT, it's as fast as I can run that day with the amount of training load I've recently done. I'm not searching for PRs, my PR days are well behind me. I don't want to know what my goal pace for a PR is. Show me where I said that. I want to have a goal pace for today's TT that tracks my fitness, or in garmin terms, its form of vo2 max. If I could downgrade my vo2 max so that it would give me a prediction that I could do today, that's what I would like. It's evidently not possible. Never mind. Life goes on.

When all of your tone posts are correcting and refuting what people suggest isn't helping.  The use of the word time trial is confusing and shouldn't be used IMO.  Attempting to totally circumvent all of the intent/programming of a watch to have it do something special for you also. 

But, as already suggested, to get what you want... lower HR max slowly over the course of many weeks/months until the race predictor is closer to reality.  But this will ruin many of the other features of watch (recovery time, anaerobic/aerobic training effect, training status)

It sure would be great if Garmin (like Strava Premium) gave training pace zones based on your imputed race PR.  Garmin does this for Power Zones where you put in your Function Threshold Power... then it gives you zones just like with HR.  Training Paces for the average person is very important and can give great structure to someone that isn't necessarily following a training plan or a coach.  Especially if the popups on each zone told a rough time at pace targets or very general workout suggestions.

It's an indication, some might run faster then predicted, some slower.

Also, from what I know it's predicting on what you could do with proper preparation and training, what is within possibilities. Not exactly what you can do now given what you ate, how you slept, the wind, the shoes your wearing, fatigue due to other stuff.

If you do some random training and end the week (after 80k?) with a time trial that is NOT what you can run. That is what you can run given the variables from that week and the week before.

In actual races you can run faster, if you prep for an actual race you don't train 70k in the same week, you might have a trainnig schedule for that race, etc.

So it does exactly what it does, give you an indication of what is likely possible. I also don't get what the problem is if it's too optimistic (apart from demotivating maybe), just ignore it.

In my case I ran my 10k over a minute faster then it predicted and still is predicting, t's not a medical device... it uses algorithms and predictions and they are overall good for most ppl. Not perfect and surely not for everyone.

It seems there's no easy way of achieving what I was asking for. Which was to detune the time/calculated vo2max so that I could use it as part of my goals for my time trials. I guess I could take the time it shows and just add a constant to it, like 2 minutes, and then make that my goal. I did a 6 hour hilly bike ride on Saturday, then took Sunday and Monday off. After today's run, it's taken another 14 seconds off my predicted 5k time, now at 20:49. Would be nice to know if that's actually theorertically possible for me. I'm a little skeptical.