This has been a slight problem for McPe since 1.8. I had to log out and log back in to change Skins I picked from Photos. When 1.9 came out I can switch skins but the confirm button is Unclickable and I still have to log out and log back in to change.
Thank you for your report!
We're already tracking this issue at MCPE-37926, so we're resolving this as a duplicate and linking it to that report. If you have additional information, please add it to that report. You may also want to upvote and/or watch that report to show your interest.
If you didn't, please try to search before reporting a bug, as nearly half of all the reports we receive are duplicates.