Hi,

In the odoo apps store there are lot of modules available for the same, but most of them seems to be paid, if you are interested you can have a look at those paid modules.

1. Product Internal Reference Generator

2.ACS Product Internal Reference Generator

If you like to do it by your own, you can check this module which generates the barcode for the product, you can make some changes to the code and assign the value to internal reference instead of the barcode. See: Product Barcode Generator

Also you can have a look at this video, which assigns a sequence for newly creating partners from the user interface itself using the automated action, you can apply same for the product internal reference, see: Add sequence to Contact's Reference with no code

Thanks