What to do if you find a bird egg ?

okay so i found this bird nest in a bush in my backyard. and the next day there was a little white and reddish/brownish speckled egg in it.. Then about a week and a half later i realized the poor little egg had been abandoned by it parents. after that i checked on the egg everyday (not touching it) just to be sure it was still there. finally today i took the whole nest out (1.5 weeks later) and i have no idea how to take care of an egg.. im not even sure if there is still life.. but i wanna find out. and like how do i take care of it? who should i call ? ! oh. and i got it down to 2 kinds of birds that might have laid the egg.. either a House Wern or a Black something Chickadee. So if there is anyone who can tell me what to do. i would really appreciate it. Thank You.