Unable to change Buyer name in Requisition Conversion program

Unable to change the username defaulting in the Requisition Conversion program. Field is grayed out. 

Purchasing

Missing Purchase Order permissions

System Administration > Security > User Attributes

1. Highlight the Role needing to be updated

2. Click Edit Role

3. Click into the Purchase Order folder

4. Grant permission to 'Maintain others' unposted PO up to/including status = Approved'

5. Grant Data Access 'Maintain others' unposted POs = Full'

6. Click Accept to save changes