I cannot delete the following question:
Most probably, I clicked the reopen button by mistake. It says
can't delete as others are investing time to answer it.
How do I delete it?
You cannot delete it as it has two answers.
You can only delete a question you asked if it has no answer or a unique answer that has not received any upvote at all, where "answer" means "answer post that is not deleted."
Tangentially, I assume that the message you reproduced says "answer" not "ask."