How do I take a build assembly and put it against an asset account as the assembly isn't being sold but kept by the company?

Hello @lisa74,

You'll want to select your Asset account as the Income account of your assembly item.

1. Go to Lists.
2. Select Item List.
3. Under Item, select New.
4. Choose Inventory Assembly.
5. Enter the name of your assembly item.
6. On the Income Account menu, select any of your asset accounts.
7. Select all your inventory parts.
8. Click OK.

Here's an article you can read to learn more: Combine your inventory items to build finished goods.

I'm also adding a reference here for ideas about how you can start tracking the items you manufacture.

I'll be here if you need more help. Thanks!