Here is the documentation: Upgrading from Mendix Studio Pro 9 to 10 | Mendix Documentation
The project/app needs to be migrated to GIT before you upgrade as per the above documentation. Here is the relevant GIT migration documentation page: Migrating to Git | Mendix Documentation
This does not happening automatically by just opening the project in the 10 modeler.
Git is required for Mendix 10. Following the along the documentation is the easiest way to do it if you haven't before.
Hi Reemali Patil,
This is step by step you can migrate SVN to git:
1) Go to your app -> Team server -> Copy app repository-ID
2) Go to https://git-migration.home.mendix.com/p/migrate-project/[repository-ID]
Click step by step on this web
3) Go to your app again and click open app in Mendix Studio Pro -> make sure clone new app in empty folder