i would separate him from some of the other degus that you may have so you can keep an eye on him
keep him in a smaller cage and try not to let him move around a lot until his tail is well and healing good
make sure you keep his cage VERY clean, since he is a rodent and he will probably be dragging his tail around, you don't want feces and other stuff to get stuck on the tip of his tail... use towels for bedding for now to prevent loose litter from sticking to the healing wound
check his tail twice a day- once in the morning as you're waking up and before you go to bed to check for infection and to maintain proper hygiene... make sure it stays super clean and keep it washed off, you could even try putting Neosporin on the wound to help it heal properly
watch his food and water intake to make sure his "owwie" isn't affecting his regular behavior, make sure you are feeding him a healthy diet, and keep it low-key for him (little handling, little moving, low noise level)- just keep it low-stress for him so he can stay happy and healthy while it heals... if he is depressed or stressed his tail will not heal as fast
if at any point his tail begins to look swollen, oozes some weird pus, or overall, just looks infected, OR if he isn't eating and drinking regularly, take him to the vet.... infection in such a small animal would kill him quickly and only a vet would be able to provide proper help to an animal with an infected wound...
just keep a sharp eye on him and watch his behavior
~ Proud mommy of rabbits, rodents, and a dog ~