Patch the data file into the deltarune copy you have in your chapter 1 folder of your DELTARUNE folder, then drop the "lang" folder into that same chapter 1 folder (this will replace the base game ones so I'd suggest backing them up just in case), and then finally, drop the "mus" folder into your DELTARUNE folder (this replaces jevil's theme so back it up if you want to change it back)

Additionally, this mod comes with a pre-made Jevil savefile that you can put in your DELTARUNE saves folder (it takes the second slot by default, you can rename it to filech1_0 for slot 1 or filech1_2 for slot 3, also it might appear a little buggy on the file select screen but that's just how Deltarune is)

(ps stole this note from JEVIL HARD MODE mod so dont snitch)