Returning call to sender

Hi All

I am pretty new to this but was able to sucessfully configure my PBX except for one thing.

I am not sure about the terminology so I do not know what to search for.

Basically, I need to do the following:

When a call is transferred to another extension and that person does not answer, the call needs to go back to the person that transferred it (after x amount of time of just ringing).

I hope the above makes sense and that some one can assist.

Many thanks.

Kind Regards,