How can i fix my FPS

Well in fact you can have a lot of "fps drop" causes. You need to see first your PC Config. After, you need to check how the ressources is used by your OS. Sometimes a good PC can be sh*t because of the OS and others programs in background. Also, check the settings of the game and at the end you can use some commands-tweak.

But first just check your config pc. This is the most important thing. Are you noobie on PC config or you are ok?