Let's say that Alice (or Bob or Charlie) realizes that she made a mistake when issuing the extrinsic, and they want to cancel it. This needs to happen before the call is finalized, and only the initiator (depositor) of the call can cancel it. Here's how:
Click on "View pending approvals," as explained above.
On the modal that opens up, click on the "Approval type" drop-down menu and select "Cancel this call hash."
Click "Reject."
This will cancel the multisig call and release the reserved deposit in Alice's account.
Reminder: Only the signatory who initiated the call can do that.