Try this stretch for a week, 3 times a day, works wonders for my knees !
https://www.basd.net/cms/lib/PA01001269/Centricity/Domain/1342/Hip%20Piriformis%20Stretch.pdf
– Go to the one, with the bench, and this text:
Standing Hip ER Stretch at Table
REPS: 10 | SETS: 3 | HOLD: 5 | WEEKLY: 3x | DAILY: 1x
Setup
Movement
Gently lean forward, hinging at your hips, until you feel a stretch across your hip and
buttock, and hold.
Tip
Begin standing upright with one leg bent and rotated outward, resting on a table or bed.
Make sure not to lean to the side during the exercise.
Cheers!