You should definitely hit the gym for some time, and get well conditioned before using any AAS. Besides, in the beginning you will already get great and fast results thanks to muscle memory.
Then, once you get in a rather good shape, you can consider using steroids. Also, it would be a good idea to start off with SARMS, since they are milder and there are no side effects with them. This would allow your body to get back into combat in a gradual and healthier manner.