Hi,
You will want to dissasemble the phone completely, after you have done this, the DIY solution is to clean the entire logic board with 99.9% isopropyl alcohol and a toothbrush, also cleaning all connectors on the other parts.
The professional way would be to take off any shields and clean the entire logic board in a ultrasonic cleaner, and then clean it with isopropyl alcohol after ultrasonic treatment.