There are quite a lot of threads on caponizing, some quite interesting to read, try 'search'ing.
Mostly the problem sort of boils down to, it is not usually feasible to have a vet do the operation (most just won't, period, and if they did it would be fairly expensive, into the many hundreds of dollars) and it is pretty risky to DIY as a once-off on a pet. If you could find an old-timer well practised in caponizing, it would be less risky, but such folks are no longer abundant.
And apparently most capons still crow, if that's what you were hoping to avoid. Mostly what you would get out of it, assuming the chicken survived (it's major abdominal surgery, since the testes are up in there near the kidneys), is a large *heavyweight* bird that could not fertilize hens. Worth it, perhaps, if you want a 12 lb roaster; maybe not so much if it is just a pet.
But, read some of the other threads, there is good info there.
Good luck, have fun,
Pat