Flip the Active toggle in the group's row on the Menu Groups page. Sprwt first deactivates every other group with the same Position for this kitchen and then activates (or deactivates) the one you clicked, so at most one header group and one footer group can be live at a time. The toggle saves immediately (no Save button). Turning a group off without turning another on leaves that position with no builder menu; the site then falls back to its standard navigation for that position.