So I think that there needs to be more advice on how to do this

There's an entire field of therapy and self-help that covers this, called radical acceptance. It isn't something that can instantly be picked up as much as something that is practiced and improved upon. Accepting the reality that the other person is not romantically/sexually interested and accepting that one's own romantic/sexual tensions will not be fulfilled to that person leads to a release of tension and the growth and flourishing of other positive emotional experiences that can then happen with that person. They won't become romantic/sexual, and by that point, it won't matter to you.

There's entire libraries worth of books on the subject, and I assume a browse of the highest rated ones is a place to start. Therapists also offer basic training courses for how to observe one's lived reality in the moment, how the body feels, how the mind feels, being instead of doing so to speak.

If it is too much for someone to be friends with someone after a romantic/sexual offer is turned down, so be it, but being honest and forward about how that feels is the best thing to do no matter what happens next. The worst choice is to try to remain "friends" while hoping for some kind of romantic/sex opportunity later.