Well, what's the configuration of "H" plus one electron? "H" notoriously has only one electron... and it is in the 1s orbital, the first orbital of n = 1 and l = 0. Therefore, its electron configuration can only be 1s^1.
...and "H"^(-) has 1 + 1 = 2 electrons by conservation of charge... so 1s^? is the electron configuration?