Hi there, yogi4.

Using QuickBooks Online Advanced, you can customize the fields on Purchase Order. 

To get started, let's turn on purchase orders for your company. Here's how:

1. Go to the Gear icon at the upper right hand. 
2. Choose Account and Settings. 
3. In the left menu, tap Expenses.
4. In the Purchase orders section, select the ✎ icon.
5. Put a check on the Use purchase orders box.
6. Enter titles for the custom fields. 
7. Tap Save, then Done. 

For more details about this process, see these articles:

• Create and edit custom fields in QuickBooks Online Advanced
• Create purchase orders in QuickBooks Online

Drop a comment if you have any additional questions. I'm just a few clicks away to help you. Have a nice day.