Hello and welcome to the forum.
It's good news - you can download and install the (free) AmpliTube Custom Shop. That will then let you use the Fender gear models.
Some notes:
1) the AmpliTube Custom Shop installer installs 3 products: the AmpliTube
- the AmpliTube standalone program and plug-ins,
-- the Custom Shop standalone program (for AmpliTube, T-RackS and SampleTank),
-- the Authorization Manager standalone program (for many IKM products).
The AmpliTube Serial Number(s) that you have determine which gear models are available by default.
2) Download it and install all 3.
3) Just in case, install the latest Authorization Manager, from here:
https://www.ikmultimedia.com/products/authorizationmanager/4) Run the Authorization Manager and enter the Serial Numbers for AmpliTube Custom Shop and for the Fender collection. Both numbers will be in your IKM Account User Area / My Products section.
5) Run the standalone Custom Shop program, login to your IKM Account, select the AmpliTube tab and click [Gear}, then "Restore my Gear". Now you will be able to use the free gear and the Fender gear that you have purchased. You can, of course, try out any of the other gear models too.
6 Run AmpliTube (standalone) or in a DAW and off you go.