can you repeat bellows breath on 1 unit?

Yes — pay the [Repeat] [1][C] cost and the second execution of the effect can choose that same unit again.

A single instance of Bellows Breath can't hit the same unit twice, but the repeated execution is a separate set of choices, so picking the same unit is legal (Rule 820.2.a). With 1 Might, the unit takes 1 damage, then another 1 — it isn't defeated until Cleanup runs after the whole spell has finished resolving, so no heal or shield effect can save it "between" the two hits. Note Repeat can only be paid once per instance (Rule 820.1.c.3), so 2 damage is the cap here.