Where is GSM Module?

Hi all,

where to look for GSM Antena Module? My P20 lite after droop into water stopped to connect to any GSM network. What is weird my WiFI is working fine and every other feature of my P20 lite. I cannot search and establish connection with any GSM signal. (no signal). I don’t know what to replace, mother board or maybe microphone/usb board which is situated at the bottom of mobile phone. For sure one of them is broken. I don't know which one.

Thank you in advance,

Marek