“On hold” and “closed” are the same thing. The annotation on a closed question changes from [on hold] to [closed] after 5 days. I've never understood the rationale behind this name change.
If a question is edited during the 5 days after it was closed (i.e. when the annotation still reads [on hold]), it enters a review queue for reopening. The question stays in the queue until either it gets reopened or enough people vote to leave it closed (“leave closed” votes can only be made from the reopen review queue, not from the question itself). This only happens after the first edit, so it's only helpful if you get the question update right the first time.
If someone has left a comment on the question and you've edited the question in a way that addresses their edit, you can reply to their comment. When someone stated a reason for closing a question in a comment, they'll usually vote to reopen if that reason no longer applies to the edited question.
If the question doesn't get enough attention but you think it should be reopened, you can request more eyes in chat. On this site, there are only two users who frequent chat, in separate rooms, so chat isn't really effective.
If it's a clear-cut case, you can flag the question and request that it is reopened. Flags are handled by ♦moderators and they can reopen a question single-handedly. Since this bypasses the community decision process, please do it only when the situation is clear.
If there's room for debate, you can ask a meta question to initiate a discussion on what should be done with a question. A meta question about a single question is a bit overkill (usually we have meta discussion about a whole class of questions), but we do have a specific-question tag on meta for this sort of things.