Knee Problems When Lifting Leg

I posted this already in the article discussion regarding eccentrics, but looking for more advice really as I’m sure its quite a simple question! Thanks

->I have a problem with behind the knee tendonitis ( I think ). I get a sharp pain which feels like something moving or twanging past something when I do an upward kneeing motion. (As in motion of kneeing somebody.) What exercise can I do at home to help this?! I’m actually slightly unsure what the eccentric part is in exercise terms for something behind the knee lol… I am thinking it may be because I’m too quad dominant, and was considering squatting down on the bad leg slowly, then using my other leg to help with the squattin “up” part. (akin to the article which says use a leg press machine and push the weight up, and then just lower it with the ‘bad’ leg.

Am I correct? Or am I totally wrong lol… Any advice welcome, Thanks