Work on the basics even if you already know them. Get a trainer
Do a lot of flat work and trial rides to get used to the feel again before you fully get back in and that helps instill more confidence!
I completely agree with what the others have said. There was a girl at my barn who broke her arm and had to take a couple months off, when she got back she did a lot of ground work, flatwork and poles will be your best friend for a while haha. Don't feel pressured or rush too quickly into anything. Take it easy first couple of times but also make sure to challenge yourself even just a little every time so you can improve and get back into it.
spend some time around your horse and go back to basics for a while. Even walking on your first ride is fine and then slowly get back into it
start slow and dont rush! when u get on for the first time, just sit and breath when ur ready start walking and eventually trotting and cantering when your ready! dont forget to breath!
Just start slow, try to spend some time with the horse you’ll be riding to boost you confidence. Maybe try stretching or exercising before you ride to loosen up. Hope this helps :)