Remove Domain Controller and create new domain

Hello,

I am new to configuring domain controllers.

Here is my current setup.

I have 3 domain controllers on the same domain across 3 different networks. They are all failover and replicated together.

What I want to do is remove one of those domain controllers from the exisiting domain and create a new domain. What is the best way to do this? or is there an easier way than to remove it completely from the current domain?

Thanks!