Stop over thinking what to do
Bend your knees against resistance.
Start slow.
Progress gradually.
Physical adaptations happen over weeks and months.
Build up the point where you can work hard.
Here's a basic program that seems to work pretty well for my clients:
Warmup ~3-5 minutes. An easy version of the same exercise is usually perfect.
Do 2 sets every other day at a height where 10 reps is tolerable.
When you can build up to 2x20 reps pain-free, lower the elevation slightly and work back up in reps.
Never exceed a 2/10 pain.