Help I just found a kitten

Hello all, My brother found this kitten by his place of work and I brought her home into my bathroom with a kitten litter box. I tried to feed her some milk replacement because I’m not sure how old she is, but she is small. I also got her kitten mousse.

Any advice is needed and welcomed. I plan on keeping her as I already own a cat and wanted another. I tried taking her to my vet but they couldn’t help me and told me to call the non emergency line to get her adopted.