Hi @lesegomolete
The screen is faulty and needs to be replaced as it cannot be repaired.
Here's a [https://www.youtube.com/watch?v=ExGSpQZv4AI|video] that may help.
''***Note:*** There are two Galaxy A12 models and they use different screens. If you get the wrong screen it won't work''.
The Samsung part number for a Galaxy A12 (***SM-A125F***) LCD + digitizer module is GH96-14116A and the part number for a Galaxy A12 Nacho also known as a Galaxy A12s (***SM-A127F***) LCD + digitizer module is GH82-26486A GH82-26485A (for the BOE flex version) or GH82-26925A (for the LTPS flex version).
Check what model number that your phone is and then search online for the part number applicable to your model.