What should the questioner do after feeling guilty for participating in selling subscriptions for design programs through an online store whose owners have started not solving subscribers' problems?

There is no guarantee required from you concerning what happened with the programs you marketed, as long as you were merely an intermediary pointing those interested in purchasing to the store, and no deception or fraud occurred on your part. This is because an intermediary is a trustee for both parties, and a trustee is not liable unless they transgress.