How to reuse incoming req value in outgoing req?

I have setup a mock server. In the URL of the incoming request and in the body of the incoming request, there is a value that I would like to reuse in a subsequent outgoing request.
Is it possible to save the incoming value in a collection/environment variable and use it in the outgoing request? Please note that Iā€™m not talking about the outgoing response, but outgoing request.

Example:
Incoming request URL is ā€¦/{{session_id}}
Incoming body is in JSON format. One of the properties has the value {{session_id}}.
The body of the mock response is empty.
I need to send a request subsequently with this session_id in it.