Upvote:1
A credit with Airline ABC is credit with Airline ABC. Airline XYZ isn't going to accept that credit, and unless ABC regularly sells flights from XYZ via their website, ABC is unlikely to sell you a ticket for XYZ.
Airlines have been struggling through this time of reduced/restricted travel, they do not want to refund you so they issue credits instead. Buying a ticket from XYZ means that ABC needs to pay for that ticket. They'll lose any profit made on the sale, so really it ends up being no different that if they'd offered you a cash refund.
So no, unless they already sell those tickets for another airline directly, you're not going to be able to use your credit with another airline.