Everyone should learn to easily identify their stabilo line. On most gliders it is the outer B-line and has, very often, a different colour than the other lines on the same riser.
This is not a tip on recovering cravats in the air using the stabilo line (hopefully your instructor has given you that information).
But you can use it on the ground:
A typical scenario is a wing tip has folded towards the centre of your wing and has caught in some lines, as a result of an aborted launch or wind change. You have in effect a Cravat on the ground.
Either some kind soul pulls it out for you, or you can look much cooler by sorting it out for yourself. The trick is to build a small wall first and then pull on the stabilo line and out it pops!
Try it – it works for me