I think the idea is that, when you're judging yourself really hard for something you've done, you're asked to consider what you would think of a friend who had done the same thing. A lot of the time people would view the friend as having a made a forgivable mistake, even though they're treating the behavior in themselves as evidence of an irredeemable and permanent character flaw. So it's like, use supportive language when you talk to yourself. Remind yourself of all you've done right and all you've overcome, that sort of thing. Forgive yourself and build yourself up. It's a specific instance of the kind of labeling-and-countering you're talking about.