Like Capt. O said.
For pressed down casebacks there is a special knife often used. Be gentle when using this or else you might damage the case.
For screw down case back there are there common options. The rubberball, the vaccum tool and the plain rubber glove. The last one not so many use but it works quite well.
All tools mentioned are cheap and can be sourced on ebay, Ali, Amazon etc....
- Vorenus