could not change the name of the requestor in iProcurement

Hi Gurus,

We have a situation, where from each department one person say Mike will create requisitions in iprocurement on behalf of others.

When Mike logins to iprocurement, he can see his name as requestor.

Now if Mike is creating the requisition on behalf of Amanda, Mike should change the name of the requestor to Amanda.

Now when i click on the requestor List Of Values, i could not change the name to Amanda. All i can see only Mike. No other names.

Am i missing any set up ?

How can this be achieved ?

Thank you,

Amanda