You have to type very quickly, without hesitating.
When using the command "Image > Adjust Date &Time", click into the year, use the delete key to erase all digits, then the new year number in quickly.
If the date is reverting, Photos may not yet finished to file the photo correctly in the Photos Library. Wait a bit, after importing new photos. I would try to to change the date while viewing the photo in the All Photos album, not in Recents or Imports. Once the photo appears in All Photos, Photos has indexed it properly in the Library. Right after importing the photo, Photos may not have finished to file it in the Library and ist may still be updating with iCloud. Sometimes it helps to restart Photos, to force it to update the library and save all waiting changes and updates.