Front Camera completly not working (black )

Hello guys!

I have recently brought back to life XS Max.

The original one was completly destroyed but the motherboard and other components except screen, back glass and charging port. Ive decided to put everything together by composing two into one phone.

After putting everything together I have notoced that the front facing camera is out of order. I tried other two cameras but those two are just showing the last image of the rear camera and focusing and blurring and so on. I have tried everything: DFU, hard restart, deleting other aplications which uses camera etc. So the question is: What is causing this malfunction or where should I look for?