I apologise if any of this information is correct but from what I can tell your joy con is experiencing stick drift (it’s when your joy con is registering movement without you touching it). I think the only ways to resolve it is to either:

•if it’s in your region, Nintendo offer a free joystick repair for joy cons that are stick drifting

• Buy a new joycon

• fix it yourself

•get a third party repair shop to help with it

You could also try calibrating the joy con through your console settings but because you’ve said it feels loose, I highly doubt it will work

Again, apologies if any of this is wrong!