If the file you’d like to restore to a previous version is still open in Illustrator, you can try using the Revert function. To do this, go to File > Revert. This will revert the file back to its last saved state, and cannot be undone.
Alternatively, if you have File History enabled, you may be able to restore an older version of the file by right-clicking it, then going to Properties > Previous Versions.