Customer Hierarchy - Remove Level 1

Hello,

I've create a customer hierarchy with 3 levels, but finally I need to remove the 1st level.

I entered a date in the past in the "end of validity date" field but it the whole hierarchy is now "deactivated". I can't even re-enter another date to reactivate it.

So my questions are :

- How can I reactivate the hierarchy

- How can I remove only the level 1

Thank you !