My Imac screen is black and i don’t know what to do

So, my external display on my mac stopped working so i tried t find solutions. I stumbled across an app that allowed you to change the resolution On my mac. I thought it maybe could help with the problem so i downloaded it. Whilst i was configuring settings, i clicked the “Change resolution button” and it brought me to a screen where i could choose a resolution. My dumb self clicked the 1440 x 1080 without thinking it about it. Now my screen is totally black. Ive tried to restart it many times please help.