It may just be that, with an adjustment to your existing retainers (assuming they are hawleys), or with a new retainer, a slight adjustment could be made. Yes, I'm guessing you'd need 24/7 wear for a bit, to move the tooth.
As ever, your ortho is the one who can advise you, and I'm sure there is an actual, or implied, warranty, that as long as you wear your retainers as advised, then your teeth shouldn't move.
(What sort of retainers do you have?)