I was in that situation a few months back!
Just be very calm, quiet & slow, but not too quiet because the cat needs to know that you are there and you don't want to scare it or anything. Provide it with food and if it starts to eat the food, try to stroke the cats head, if they get scared and back away, it's fine, it can take a long time for a cat to build trust with you. You need to be patient.
You could also try playing with the cat, nothing too big or noisy, it could just be a bit of string that you drag across the floor. Good luck!!
Ask me if you have any questions or need any help.