Hello, does anybody know please how to manage changes in Resource Plan of the Project?

I prepare project which is going to start for example in 6 months from now.
I create couple of Resource Requests in Resource Plan. The Requests are approved (completed) by Resource Manager so the resources (designers) are "blocked" for the project.
Imagine after two months from now the situation will change and I need to move start of the project 2 months later.
How to update Resource Plan (resource requests) to "unblock" previously requested and approved resources?
Completed Resource Request cannot be updated or deleted by the Platform.
Thank you..

Project ManagementResource PoolsResource Management