This is how we fixed our daughters broken 3DS XL game slot. We are not really youtubers, so sorry for the bad production here. We just didn't see too many posts on how to fix this, and I am sure there are other parents or gamers out there that wouldn't mind knowing this fix.
Our nephew shoved a game the wrong way reeeally hard jamming the cartridge lock mechanism. Any inserted games would immediately eject. It is probably important to check first if the games will still run before going to far with this method. If you can manually hold the game in place and the game will still play, then give this a shot before a warranty case.
In our case it was a spring in the internal game slot. You will need to break down the back cover. Fairly simple to do, we used an eye glass kit that had a range of tiny Phillip screw drivers. There is a ton of videos on youtube on how it is done.
For the fix, really all you are doing is repositioning the spring with a screw driver, then, while still holding the spring back in place, push a game cartridge down firmly. This should force the spring back to its native resting place.Test with a cartridge or two a few times while everything is still in pieces to make sure it stays put.
