Big thanks to motionarray.com for explaining this:
https://motionarray.com/learn/after-effects/loop-video-animations-after-effects/
1. if your footage is the correct length, you can go to the projects panel right-click the element and select Interpret Footage > Main. in the dialogue box just select how many times you want to repeat it
2. Remapping Effect. Enable time remapping, option+click the stopwatch for time remap, Using the add Menu select Property > loopOutduration
If you need only a portion of your video looped… create a precomp of your footage, then use option 2 on your precomp. Just make sure the precomp is the right length to get the loop to match up correctly.
The loopOutduration command doesn’t seem to indicate where loops begin or end… But you want that on your first frame of the loop. ignore the other keyframes.