Knees tend to cave in when the feet are rotated out too far, so I’d start by looking at that. Depending who you talk too, you may hear 30deg max ext rotation is OK. Others will say 10deg max. Personally, I’m more in the 10deg camp, but not for everyone. Some of it depends on your height, femur lengths, etc. But if your foot position is good, then I concur that the first corrective is to take weight off the bar. Then progress in smaller increments, always maintaining your knee alignment.