This is barely three pages back: https://www.flyertalk.com/forum/marr...come-gift.html

You tell the FDA you were not offered the welcome gift at check-in and would like the welcome gift guarantee to be honored. LIkely you'll have to talk to a manager.

I've gone about it two ways:
(1) At check-in, wait until the check-in is done and ask "is that everything?" and if they say "yes" then I mention the welcome gift was not offered and that I'd like to receive the guarantee. Usually here they look dumfounded and say you'll have to talk to a manager (who may or may not be present depending on time). If not available, the FDA will likely go into their system and make a note saying they offered the welcome gift, leaving you with little recourse. I usually then ask the manager if it's normal they make that note (to which they look at you weird) and add "that's what I thought. The note was added only because I asked about the guarantee after check-in." Either way, you're in for high blood pressure and they'll likely refuse, claim they offered but you didn't remember, say they have the choice not you, or that they're special and exempt.

(2) Later, after check-in, try to claim you weren't offered the option of points or gift. Usually they'll just claim you misremembered or claim they don't offer a choice either because it's their choice or beacause they're "exempt." In either case, frustrating.