go in smartly dressed.
dont get angry
take both forks and all proof of the work, receipts etc, have all the details of the work, ie who did it and when, times, who you spk to, clear in your mind.
spk only to the manager/owner, have the DT contact details for returns/ ie steerer replacement with you and give it to the manager.
TELL him you want both steerers replaced within a month and give them deadlines, blag you have a holiday coming up.
be prepared for a sharp intake of breath, and manouvering, but you would be amazed what a confident manner can accomplish