How to dial-out/outbound call within the conference to join that person?

Hi All,
I have created the conference by using Admin and User pin.
When Admin joined the conference, how admin make dial-out/outbound call within the conference to join that outbound call person?
What are ways to do this?

Is there any other ways to do this?
How it will be done in the FreePBX?

Please help me to do this.

Waiting for positive reply.

Thank you.

Kapil