You can move items between sections, either one-by-one or in bulk.
Moving individual items
To move an item from one section to another, click on item options ("..." icon) and select "move to section".
You'll then see a list of all the available sections on your board. Click to choose the section you'd like to move your item to.
Moving items in bulk
Press & hold "shift" and click on an item to open the bulk selection panel. Click on all the items you'd like to move.
Select "More actions" ("..." icon) in the bulk selection panel and select "Move to section". You can then choose the section you'd like to move your items to.