Need Workout assistance: Walk 1km then do 30 Push-up. Repeat until activity is completed.

Just start a run activity with 1km alerts. 

This is what I'm doing presently, but then the push-ups are not recorded, only the walk.

create a multisport activity alternating between walking and strength training. Put in a 1 km alert/autolap for the walking.

Didn't know about this feature as I was stuck on creating a workout via Garmin Connect.
Will give it a try, seems like you have to do the edit from the watch itself.
Thanks

Yeah, the workouts are single sport only. Yes, custom multisport is on the watch.

Was straight forward.
Choose "Walk" as 1st activity, then "Other" as "strength" was not part of the listed activity.
Not having "Strength" as an activity choice defeats the purpose of this initiative as I wanted to record the Push Up effort on top of the Walk

I will test it tomorrow and eventually communicate with Garmin Support as to why "Strength" is not part of the multisport activity. 

I just checked this myself, and you are quite right - I can't select Strength as a multisport option either. Oddly, I can select Pilates.

Multisport stuff doesn't really get entered into seprate training load buckets for viewing in reports etc... so even if you could create it, it would be messed up.  Strength and Cardio workouts would also possibly be good... but then your walk would be sort of ignored (you would get 'miles' but in the wrong category).   

Personally I would do it either as a walk or strength...  personally probably strength as this is a pushup workout primarily.  That will get you the the data in your strength training section of report.  for monthly load etc.  Then just do the recovery walks until you press lap button. Then enter manual walking activity in garmin if that is part of your recording / training logging.

or alternately just record a walk with watch with autolap at 1km or a programmed workout with 1km walk, then pushups (other) until lap press, 1km walk...repeat.   Then manually enter a strength workout with ## pushups for total time of the pushup laps.  Could also pause watch during pushups to prevent accumulating 'walking time' while pushups (since you will enter pushups in training log manually).

You can do an automatic multisport activity. Start a Walk, have autolap or distance alert set to 1 km, when alert comes, switch sport to Strength, do your push-ups, switch sport to Walk, the distance starts from 0 again and your alert will come again at 1 km. Repeat.