Record Not Updated In Table

New member, so forgive me if this has been covered before:

Trying to build a Business database (more for the exercise than any desire to run a business) and have the following problem -

Have a Purchase Ordler Line table and an Item table - the item in the PO line is a lookup from the Item table - I want the PO line price to default in from the the item table.

Created the query and generated the form & subform - on screen, the substitution works, the PO line price does get picked up from the Item table, but the PO Line table does not update with this value.

Is there a soltion to this?

Any assistance gratefully accepted