Change Image layout for existing posts

Hi,

I have a private UPG gallery (only for logged in users) and I recently changed to using a personal layout for the individual image pages.

My problem is that only newly created posts use the personal layout, not the existing posts.

Is there a way to change all the existing posts in one go?

Selecting the posts and choosing edit doesn’t give a choice to change the Image Layout!

I looked at the database in myPHP but I can’t see a field for Image Layout on posts with type UPG.