I have a Joint Brokerage account with a friend. How do i notate in Turbotax that we each own 50% of the account (each contributed 50% ) ?

Me and my friend have 50% on a joint brokerage account.

On the 1099-b its both our names.

How do we each notate in turbotax that we own and are liable for 50% of the tax ?  I know we are supposed to put a note on our taxes somewhere but i dont see where. 

Thanks