How can I separate creating a requisition from approving a requisition with menu setup or function e

For segregation of duties, we want to set up a responsibility in Oracler R12 (iProcurement) to enter a requisition, and then setup a responsibility to approve the requisition.

Using the seeded menus, we created the 2 responsibilities, but the approver can still enter a requisition. How can I remove the access to the Shop tab for the approver?

When that is set up, I also want to create a responibility to receive the goods. Again, I need to remove access to the Shop tab.