Loosens, as a shoe

UNLACES

Think of what you do to a knot before slipping your foot out.

"Loosens, as a shoe" hints at the action of undoing the laces to make a shoe less tight. The answer "UNLACES" combines "un-" (meaning to reverse an action) with "laces," which are the strings used to fasten shoes. It’s a straightforward verb that describes exactly what you’d do to loosen a tied shoe.