"a restart is necessary to apply some settings"

hello, im new to overwatch, always wanted to play it since i was a kid back in 2016 but my pc sucks. Depending on where i look the fps will drop dramatically and i need to change my graphics to low but when i do, the red 'you should restart' message at the bottom shows up and im like "restart what?" ive read youre supposed to just close and open the game but the graphics still look the same and and so are the videos settings. doesnt matter how many times i open and close the game the graphics go back to medium. i dont know what i am supposed to do. thanks for your patience