There is not way to rollback the changes. The only way to restore it is by overwrite it once more with an old version.
You can get any version of the process/project you want, becuase BP keeps the history of changes.
In the Studio tab, select the process/object in question. In the history of changes, select the version you want to recover and the newest version together(ctrl + left-click).
Right-Click on and select the Compare option.
In the new window, In the File menu select Export Right/Left Side (whichever is the right version for you) and then export it.
Now, you just have to inport it and done.