I'm answering the general question, not this case in particular.
If the answers on a dupe are better than the ones on the original, one option is to nominate it for merging. This combines the questions into one (the person doing the merge dccides which question to keep) with all of the answers.
I believe this leaves the dupe question intact, with an annotation saying "merged into (link)". It's possible that I'm mis-remembering and the merge deletes the dupe. If so, and if the dupe is valuable as a signpost, then it's easy enough to undelete it afterward.
There is no way1 to move only some answers from one question to another; it's all-or-nothing.
1 Well, presumably devs could hack the database directly, but don't ask for that. It's probably dangerous and almost certainly not worth the effort.