You want to replace a manager due to poor performance. You finalize the Evaluation, document the issues and then initiate the termination. Next you have to find the replacement.
While the above method is used by many organizations, when possible wouldn’t it make sense to make sure you have the replacement first?
There are times it’s more important to get rid of someone quickly (such as if illegal or unethical activities are involved) but when you have the choice, work on having a replacement before initiating the replacement
Have a great day!