A hyphen is used to join a prefix, such as re, de, anti or non, to a word to change its meaning: re-apply, de-ice, anti-clockwise, non-negotiable.

Is reapply one word or two?

reapply verb (ASK)

How do you write reapply?

In the first paragraph, state the name of the position you're applying for and how you heard of the open position. In the second paragraph, explain when you applied for the position before and why you've decided to reapply. Include details about the experience you've had since you applied before.