Pain in front of knee cap when try to bend it. how should i treat it?

The treatment depends on the diagnosis. You need to be examined and a plain X-ray of the knee at the least.

Anterior knee pain without any other symptoms of tightness like difficulty squatting, climbing stairs, getting out of a chair or balance while dressing, is rare. Talk with your Doctor about your morning stretch and exercise, as well as any falls. With the big picture you should do well.