I want to make a "non-inventory part" to an "inventory part"

Welcome to the Community, Tyler.

If an item is an inventory, non-inventory, or other charge item, you can change its type in QuickBooks Desktop (QBDT). However, we can do that only for a few items. Actions are irreversible if you switch an item to Inventory Part.

To change an item type:

1. Go to the Lists menu and select Item List.
2. Double-click the item you want to change.
3. In the Type dropdown, select Inventory Part.
4. Click OK.

Please check out this article for further details: Add, edit, and delete items.

Moreover, QBDT adjusts inventory amounts and values when you keep track of each purchase and sale. However, we'll have to record an adjustment to maintain an accurate inventory status. 

If you have any follow-up questions regarding inventory items, please let us know through the reply section below. The Community is available 24/7 to assist you.

@JaeAnnC  RE: If an item is an inventory, non-inventory, or other charge item, you can change its type in QuickBooks Desktop (QBDT).

Huh? You cannot change the type of an inventory item.