One cannot just replace the whole front camera module when fixing an iPhone with Face ID.

The old Face ID part needs to be kept as it's uniquely encrypted to the device.

Here's a step by step demo working on a iPhone 13 Pro Max front camera flex.

Step 1

Cut the metal frame to remove the old camera from the module.

Step 1.2

Using a heat gun to melt the glue (works best at 200 C), and take out the old camera.

Step 1.3

This is how it looks after the removal.

Step 2

Repeat the same procedure to extra new front camera from the new module.

Step 3.1

Now it's time to mix the ingredients.

Add super glue to the corners of the original module.

Step 3.2

Add the new camera to the original Face ID.

Put it back.

Working now.

This is how to change add front camera back to old Face ID module. 

For other models it is roughly the same but can be slightly different.