You can bulk add items to a Set or bulk remove from a Set.
The following demonstration is for bulk actions on the Library view, but the process is the same to add Cards to a Set from a List, Board or Kanban.
1. Open the Library 
from the sidebar.
2. Select the items you want to add to a Set. The bulk actions menu will open.
3. Click the Set icon 
on the bulk action menu.
4. Choose action:
- "Add to existing" - will add the items to any Sets you select, without removing them from any existing Sets they are in.
- "Replace all with" - will remove them from their existing Sets, and add them to any Sets you select.
- "Remove values" - this will remove the items from whatever Sets you select.
5. Select Set(s).
Click "Save".
For detailed information about using Sets see the "Sets Help Guide ".