Delta lounge- Hack for guest pass reimbursement?

We recently traveled and had a long layover so we stopped by the Delta lounge. My husband has a plantinum amex card but I don't, so he gets in for free and my pass was $50. The guy checking us in said we could get reimbursed for up to limited number of guest passes during the year if we make Delta our #1 airline (somewhere?) and then do something else.... but I don't recall the steps he told us to take. Can anyone help?