That's kind of a tricky question but usually if a tank in low level dungeons isn't able to keep hate on one enemy they probably don't have it on the rest of the pack lol.

If the enemy you are fighting is almost dead, it's best to just finish it off so it's less incoming damage but aside from that it's probably better to stick to auto-attacks for a moment until your tank cements hate on themselves, assuming they are playing their class correctly.