Here "mouths" and "hands" represent the whole person. Alternate translation: "have done what you promised to do when you said" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
This is an ironic statement. Yahweh does not really want them to fulfill their vow to a false goddess. Yahweh knows they will not listen to him so he tells them to go ahead and do what they want. Alternate translation: "Very well! If that is what you want to do, then go fulfill your vows and do what you promised to do" (See: [[rc://en/ta/man/translate/figs-irony]])