Hi Lian,
As far as i know you can’t do that on the Mendix Team Server. If the SVN repo is over 3.5 GB, migration with history isn’t possible.
You could host your own Git and migrate manually, but that’s complex and not something I’ve tried myself.
A practical workaround: create a new app, import the latest version of your current one, and migrate that clean app to Git. Keep the original SVN app on Team Server renamed to _old so you still have the full history there if ever needed.