What Setup and configuration is needed if Creator only is approving the Purchase Requisition?

In oracle r12.1.3

Application: Purchasing

We have the requirement to configure the, Approval system of Purchase requisition.

Where creator itself on creating the purchase requisition , itself he can approve the purchase requisition.

We are trying the following steps.

a, Creating Purchase requisition.

b. Clicking approve button

c. status remain - > Incomplete

d. the approval assignment and assignment group

document type all setup are completed but still , we are having the notification - No approval found.

Help is needed.

Thanks in advance