Copy the folder containing the face files (usually named with Mbappé's player ID) to your livecpk directory:

The face mod by Sameh Momen is typically available through community modding sites like PES-FILES.RU. Sameh Momen Compatibility: PES 2021 (PC) and PES 2020

PES 2021/sider/livecpk/Faces/Asset/model/character/face/real/ .