If you are wanting to do an add-on like MAX, please see this FAQ for assistance. You are already at the highest level of product we offer:
https://ttlc.intuit.com/replies/4842241
If you are wanting to add Turbo Tax Live Look:
https://ttlc.intuit.com/replies/6419943
[Edited 04.17.19 3:19PM CST]
OP is already at the highest level of TT.