You'll need to install the latest version of QIIME 2 (2024.10) to make use of get-silva-data
for SILVA v138.2.
Or simply follow the tutorial, using your current version of QIIME 2, to download all the files required. There are several... click on the The gritty details, menu to reveal the detailed instructions... It should work if you simply replace '138.1' with '138.2'.
-Mike