How do you unpair your iPad from your iPhone?

An iPad should never pair to an iPhone.

Explain your exact starting situation, operating system version numbers, hardware model names or numbers, what you’ve tried, what you’ve seen, what worked, what failed, why you’re trying the things you’ve tried, etc.

Your iPad and iPhone are unlikely to be “paired” in the technical sense - but may both be signed-in to Apple Services using the same AppleID.

What precisely is your aim or intention? With the benefit of a more information, specific guidance can be provided.