Hi and welcome!
Could you post some photo of your rabbit and what you already have for him/her, your setup or where they live, what food you have there etc.
Sure you can spay/neuter your rabbit, you can go to vet clinic for first general check and make an appointment for neutering, they usually neuter/spay from 4,5-6 months but it depends on vet, also make sure your vet is rabbit-savvy, there's a list of rabbit vets in this forum so you can find one near you. Fixing is not cheap and vets are not cheap at all so you can try sexing your rabbit yourself with our little help.
It is not very rare unfortunately, I have one rabbit was dumped near shopping centre just left in a cardboard box in January last year, good people found him but they have dogs and kept him in a shed for a week or so and then I took him in. He is an excellent rabbit was much stressed but now he's perfect. First I thought he's very old and ill that's why he was dumped but now I think he was about 3-4 months old as he grew up a bit, he was just very scared and was staying in his corner not eating/drinking for first week. Now after one year he's very very good rabbit, very tidy and well behaved. He's still not neutered as I see no need for that, he has no problems with his toilet or aggression, not spraying etc so he's not altered.
Lots of rabbits being dumped after Christmas is over unfortunately.
