Hi Iris,
Are you using Studio Pro for Mac?
In the Windows version, you'd have a taskbar saying File, Edit, View, etc. On Mac, I believe that should be located outside of the Mac window. If possible, can you select View > Reset Layout at the top of your screen?
Hi Iris,
You can revert merge changes from version control within mendix studio pro and choose the version before your version.
** Kindly accept my answer if it assist you to solve your problem.