In the past, I've made the pieces mechanically fit together, like snaps or puzzle pieces. Glue works great for most things too, though I haven't tried it with resin yet, only with ABS and PLA.

I haven't tried this, but I suspect you could use some extra resin as glue. Apply it to the surface, then cure it with a strong UV light. I'm going to be testing a UV EEPROM eraser as a way to cure undercured prints.