after I joined with a family iCloud plan, how can I cancel my individual plan?

Lampslight wrote:

after I joined with a family iCloud plan, how can I cancel my individual one?

You don’t have to do anything. It is all automatic. See -> Share iCloud+ with your family - Apple Support

“If a family member is already paying for their own iCloud+ plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.”

Hello Lampslight,

We see you have a question on how to cancel your iCloud storage plan, we'd be happy to help.

This page here will have the details needed to cancel your iCloud plan: Downgrade or cancel your iCloud+ plan

Cheers.