Hi Shaik,
The best thing to do if the bird is still alive is to return it to where you found it, if there are still adults around. Fledglings are rarely abandoned – the parents will be nearby to help it when needed. If you cannot return it to the wild, please find a wildlife center that will take it. They will take care of it and release it back to the wild. As with all native and migratory birds, the Chimney Swift is protected by Federal and State laws, so it is illegal for you to have it. Chimney Swifts do not fare well in captivity because they will not self feed and have to be force fed. Chimney Swifts only eat on the fly – meaning they eat in mid air while chasing insects – mostly mosquitoes. Sadly this bird is going to die in your care because you cannot provide what it needs and will not know how to force feed it without killing it. Please act quickly because they cannot go very long without food.
https://www.nwrawildlife.org/page/Find_A_Rehabilitator
Brenda