how can i use the databse that i already have got with entity7 in uwp?

I have always seen that in all tutorials, databases are made in the form of code-first, but already there is a sqlite database that I want to use in my project. and I want to use entity 7 too. to do so, I made some classes from my database by means of a dll but it didn't work. in fact, I made these classes so that I could use my own database. I didn't want it to create a new database. Any suggestions? can you recommend me any links, because i couldn't find any useful link.