Get your taxes done using TurboTax

My family bought a 5 return TT Home&Bus Download from Costco.  It is the PC version.  Return#1 used the link and key to download it to their PC.  Return#2 (a mac user) used this link https://turbotax.intuit.com/lp/ty19/desktop/access-my-downloads/ to get to a place where they had to enter their TT account, then they got to a link where they could enter the key and get the software.  I am Return#3 (also a Mac user) trying to download on to my computer. I cannot seem to find a place where I can get to download link that does not require a TT account entry.  I don’t know the accounts of the two prior users, but when I enter my TT account and try the key, it tells me that the key is assciated with anouther account. How can I get the software?