Hello Alan,
First of all, I would advise using Greengenes2 instead of Silva: this is a more comprehensive database of V4, tutorial here Introducing Greengenes2 2022.10.
If you still want to do SEPP, just go to: Data resources — QIIME 2 2023.5.1 documentation. The tree for SEPP wasn't updated since 2016 though.
Cheers,
V