This is a two step process.   

First: devalue the Current Asset to $0 and transfer the value to your Fixed Asset account.

By devaluing the product to $0, you are removing the value from your Inventory (keeping the item so you can move it around the company and keep track of the current location).  The counterpart is the Fixed Assets account, which will show on your Balance Sheet. 

Next: define the depreciation schedule of the amount to create a running Fixed Asset.

By defining the depreciation schedule, you will start to see the value depreciate over time, reducing the value on your Balance sheet by moving portions of the value to depreciation expense on your Profit and Loss statement.

Steps:

A. Using the Inventory Valuation Menu, find the product(s) you want to Capitalize. Click the PLUS icon to open the Add Manual Valuation Wizard:

B. Enter the entire amount of the product(s) but with a negative sign, to indicate you are de-valuing the current asset value to $0.

Note: In this example, our finished product was worth $30 based on the Bill of Materials and other construction costs.

C. Open the Journal Items Menu, view entries in the Fixed Asset Account, and filter for Asset Linked is not set. Select it and click Create Asset.

D. Select a pre-created Asset Model to use, or define the depreciation parameters, and create the Asset following the standard process you can see at https://www.youtube.com/watch?v=AZH-HDp95PE or read about at https://www.odoo.com/documentation/user/14.0/accounting/payables/supplier_bills/assets.html#assets-entries

You will then have the same functionality and reporting capabilities as if you had created this via a Vendor Bill (for Fixed Assets you buy).

Note: This asset has a 3 Year straight line depreciation schedule with no improvements recorded against it and we are reporting the first month's depreciation, even though it won't start until the end of January.