5d3 joystick knob popped off

Fortunately I found it in my car and it didn't get lost outside. However I'm wondering if to pop it back on that it has to be inserted from below, as in some disassembly is required, or if it should be able to be reinserted from above. I'm trying to be somewhat delicate with the rubber seal that surrounds it when properly seated but it looks as though it's already developed a small tear. Possibly from when it was dislodged in the first place or possibly when trying to stick this thing back in. Going to be shooting in some dusty environments in the next week and I may have to tape it over if that's all I can do.
Thoughts?