How to transform a customer software to an generic product

Hi,

I know, this is a very complex questions and I think there are many solutions.

But we had a Software project, now we want to create a generic product from this Software.

For now we use an ASP.net webapi as backend Server for accessing the data from the Datasource.

For the frontend we use react.

What are the best practise for now to "convert" it to a Product.

First of all the custom specifica for the customer must be separated. We have the idea to handle this with Feature flags (as Pattern by Martin fowler).

But how can I handle the datastore, especially when other customer wants this part of software too?

Is there any resource that can descibe the best practise pattern for this?