To action a Shift Swap, select either No Shift (no shift will be offered in return) or select a shift you wish to swap, and then click Propose Shift. The original offeree will need to review the proposed shift by clicking the down arrow on the shift in their Shift Offers.
If the offeree accepts the shift by clicking Accept Offer, the shifts will then be updated. If the shift swap is rejected, the process will then need to start again.