By no means am I an expert with Roombas, but I've dealt with them a bit. Mu advice would be to look through the following:
1) Does this video describe your problem (https://www.youtube.com/watch?v=XQV78QIg6lo). If so, and if you plan to make that fix, I'd watch the whole video through before doing anything.
2)If that doesn't help, you could look for more videos on the matter, or you could refer to your manual. If you no longer heve it, here is an online copy (https://www.manualslib.com/products/Irobot-Roomba-560-244242.html)
Hope this helps!