You would need to merge using Studio Pro using the built in version control. If you come across some code that can’t be resolved in Studio Pro, you can use an external tool like TortoiseSVN or TortoiseGit (depending on the underlying version control system you are using).
There is full documentation on this: https://docs.mendix.com/refguide/using-version-control-in-studio-pro/
Hope this helps.