How do I make sure that a user has entered everything they need prior to adding something new?

Bare with me here... I am the new lead product designer for a company, and they way an app i am working has no hierarchy... so this design i am working on is a mobile app for entering product items, in the home page there's options such as "Manage Locations", "Suppliers" and "Create Item".

When user taps on "Create Item", it opens a page where they enter the information in the form, such as "Name", "Brand Name", "Quantity", "Supplier", etc.

"Supplier" is a dropdown, where they select the supplier name, and if they don't have any it will say "You don't have any suppliers. Please Add a Supplier". So, to add a supplier, they'd have to cancel out and go to home and tap on "Suppliers", save and start "Create Item" all over again. And, Product owner does not want a "Create a New Supplier" option in the "Create Item" page.

So, how do I make sure that the user has entered ALL "Suppliers" they need prior to clicking on the "Create Item"? I don't want them to create the form, to get to "Supplier" and then have to cancel out and play ping pong between this page and "Suppliers" in the homepage.

Any suggestions and/or ideas?