Used mounts like these can often simply be turned upside down to use the other half of the back with the original adhesive still there. The stamp will need to be removed and put right side up, of course.
If that's not working, use a few small drops of a stamp glue like Hawid glue on these mounts. Other mild glues might work as well (not "glue sticks" which do not work for me), but I've had great luck with Hawid glue holding mounts in place reliably without doing any damage.
Or start over with new mounts. That size of stamps would probably take 24mm mounts. Two good sources for mounts are AmosAdvantage(dot)com and Global Stamps.
And for cheapskates out there like me, it's also easy to photocopy those pages onto slightly heavier "card stock". Around 64# card stock would match these pages. You can do copies with or without color. Reducing the contrast helps make any page imperfections less noticeable.Then three-hole punch, use a cheap "corner rounder" punch (like a hole punch) and you have identical pages.
Here's a link to this glue, but it's sold by many sellers:
https://www.amosadvantage.com/produ...mounting-gum