Flag for moderator attention. Be thorough in your flag description. Explain the circumstances and your motivations.
A question with an active bounty can't be closed/deleted. The bounty needs to be removed first.
Depending on the situation (e.g. how much effort users spent attempting to answer your question), the handling moderator may decide it's better to refund the bounty and delete the question.
But if they see the bounty is relatively advanced and/or other users already posted answers, they can also decline your flag and let the bounty run its course.
If it's early enough, trying to delete it before attracts additional attention could be a good thing. Since bounties can easily attract low quality answers that may make harder deleting the question later.
Just don't make a habit of this, some mods run a policy of "just once" for this kind of thing.