Hello,
You can use the Change Deck function for this. This tutorial explains how:
However, instead of selecting the note type as shown in the tutorial, you’ll need to select the tag or group of tags you want to move into a new subdeck.
Unfortunately, you’ll need to do this for each subdeck you want to create, but the good news is the changes are permanent, and the cards will remain in your custom subdecks.
Let me know if you need anything else! 