I have no experience. Anyway:

• learn how to make a basic website in some flexible programming language like go, rust or python (django)
• make a list of functionality of your original website you want to provide an alternative frontend for (as a start, you can expand later)
• find a way to retrieve all important data for the most important functionality reliably
• implement it into your website
• make it fancy, expand functionality, use the same webpaths for you website like as the original (so it can easily be redirected with libredirect or similar)

You can also look at and analyze the source code of existing Libre frontends like rimgo (go).