Is this just center button or the surround?
The surround is ultrasonically welded to the cover, so a fix on that would either be a new bumper cover or using something like epoxy or maybe Gorilla Glue to reattach it.
The center which is the sensor has a set of clips on each side, depending on which sensor it is you may be able to push it forward and get it snapped in.
Taking off the rear cover isn't that hard to do, your son should be able to print/export the pages from the service manual so that you can look at the instructions.
The surround is ultrasonically welded to the cover, so a fix on that would either be a new bumper cover or using something like epoxy or maybe Gorilla Glue to reattach it.
The center which is the sensor has a set of clips on each side, depending on which sensor it is you may be able to push it forward and get it snapped in.
Taking off the rear cover isn't that hard to do, your son should be able to print/export the pages from the service manual so that you can look at the instructions.
