Team A is underwater and team B has a lot of slack. The obvious solution is to move someone from team B to team A. That happens all the time in both large and small orgs. But the problem is in the team jelling. Losing or gaining a person has a jelling cost.
What if you moved some scope instead of a person? Transfer the work instead of the workers. You may have to get creative with team ownership areas for it to make sense, but that’s OK. If team A is so far from team B organizationally that transferring scope doesn’t make sense, then instead look for team C that also has slack and is closer to team A.
Worst case, try to transfer someone from team B to team A temporarily. An embed is less damaging to jelling than a transfer.