I used to patch strings in college but no longer. With rising costs, though, I may do it again!
There is a diagram on pages 40 and 41 of the Lawrence/Salzedo Method for the Harp. You can only do it between the adjustable nut and the tuning pin. Try to use strings that are as near as possible to the same diameter. It looks similar to when you grip your forearms with the opposite hands.
The strings lie parallel. Each ties once around the other. When tension is applied, the knots pull against each other. Clip any excess lengths coming from the knots so they don’t buzz against the string. Wind onto the tuning pin as usual.