Hi @Eman,
Everything you need is on the Data Resources page, which was updated to reflect the 2020.6 release.
Specifically, the pre-made SILVA 138 classifiers are here, and the files used to make them are here. If you'd like a little more control preparing a SILVA database in your own way, feel free to make use of our new tool: RESCRIPt. This was used to make the current QIIME 2 compatible SILVA 138 release.
-Best wishes!
-Mike