pretty easy. how is tether involved?
You put your strike account info in your credit card website. And choose pay from that account. In strike you select pay from cash balance or Bitcoin balance. Then just pay using the strike account numbers
nostr:nprofile1qqsvf646uxlreajhhsv9tms9u6w7nuzeedaqty38z69cpwyhv89ufcqpzamhxue69uhhyetvv9ujucm4wfex2mn59en8j6gpzemhxue69uhhyetvv9ujuurjd9kkzmpwdejhgqg5waehxw309aex2mrp0yhxgctdw4eju6t0t25cfd explains how in this video around the 10 min mark I think.
Discussion
It's not if you are from the US or Europe. But Africa Asia and South America have tether as the fiat, I think.