Notice who never gets picked for anything, then pick them on purpose.

Being picked last, repeatedly, teaches somebody that they are a cost rather than a choice, and almost nobody says that out loud. Choosing them deliberately interrupts a pattern they have probably stopped expecting to change. It costs you very little and it is one of the few things that reliably shifts how a person sees themselves.

Notice who gets skipped over in your group, then pick them for something real rather than symbolic. Do it without explaining why. Do it again the week after, so it does not read as a one-off gesture.