Welcome to the Community, JenSu.

The Action column mentioned in Kristine Mae's post is located on vendor profiles. After clicking a transaction's Drop-Down Arrow (▼) icon, you can then use its Copy to bill option.

You can also find a Copy to bill button when viewing a purchase order.

I've also included a detailed resource about working with purchase orders which may come in handy moving forward: Create & send purchase orders

Please feel welcome to send a reply if there's any additional questions. Have a lovely Wednesday!