How do I change this to active vocie?

First, can you try?

HINT: Start with this.
An EPMO project manager . . . . .

Thank you Clive.

An EPMO project manager needed to manage if its estimate exceeded 500 hours.

Will the above sentence work?

Just to give a context.

Project ABC had an estimate of 5000 hours. An EPMO project manager needed to manage if its estimate exceeded 500 hours.
No EPMO project manager was available. He volunteered to manage the project.

An EPMO project manager needed to manage a project if its estimate exceeded 500 hours.
Will the above sentence work?
Just to give a context.
Project ABC had an estimate of 5000 hours. An EPMO project manager needed to manage a project if its estimate exceeded 500 hours. No EPMO project manager was available. He volunteered to manage the project.

Any project with an estimate exceeding 500 hours need to be managed by an EPMO project manager.

EPMO project managers need to manage any project with an estimate exceeding 500 hours.

Thank you..

Sorry again: An EMPO project manager needs to manage any project if its estimate exceeds 500 hours.

This is a perfect example of a sentence in which the passive voice is better than the active voice. Your want to focus on the projects, not the managers. Avoiding the passive voice at all costs is just silly. Sometimes it is preferable.