how to lighten hair for semi permanent dye?

idk if anything can help me with this but when i use artic fox wrath semi permanent i feel that it isn’t showing bright enough due to me having dark brown hair i mean it shows up but i feel like it isn’t blended all the way and is only in certain light. i read you can’t mix developer with it so i don’t know what to do. i wouldn’t really

wanna use bleach bc i’m pregnant so i am sure if i want to do that unless it’s the only way. lmk thanks :)