My brother forgot to file taxes for his other job aswell, how can he file for that other job aswel?

[SusanY1]

He can amend his return, after his initial return is accepted and processed.  To amend a return  into TurboTax.com or open your TurboTax software installed on your computer. 

Select the option “Amend a return that was filed and accepted.” and add-in the missing information.  

You can see more detailed instructions on the amendment process here: How to amend a return in TurboTax.