Front camera doesn’t working

Assuming your replacement camera is good, that pretty much isolates the problem to your logic board.

You've tried doing a complete restore of the phone, right? You want to be absolutely sure it's not a software problem before getting into the hardware repairs that might be required. The best way is to use DFU mode which will do a complete wipe and restore of the phone's firmware. Obviously you should back up your phone first or you'll lose all the data on it.

Once you've gotten this far, the next step is to carefully check the front sensor FPC connector on the logic board. Take a magnifying glass and a bright light and examine it for any bent, broken or missing pins; bent pins can sometimes be straightened with a pair of fine tip tweezers but broken or missing pins will necessitate replacing the connector. That's a job for someone experienced in microsoldering and isn't something us home DIYers are generally equipped to tackle.

After that, the next thing to do is to start testing for board level issues. Using a diode mode check with a multimeter can tell you which signal is having issues. You need to put the positive (red) lead on a ground and measure each pin in diode mode and compare it to known good readings as shown in the picture below from repair.wiki.

Obviously if this sort of thing is out of your comfort zone, the only other thing to do is to take it to a qualified repair shop who is experienced in iPhone board level repairs.

Good luck and let us know how it goes.