In the FPS game running in the background, switch to or find the most accurate weapon. You’re looking for the gun that has the most precise reticle (most commonly on sniper rifles). Now, line up the center of your crosshair to the center of the gun reticle and firmly apply the crosshair. If there are air bubbles or the crosshair is not properly aligned, it is possible to peel it off the monitor and apply it a second time.
You will now notice that as you switch weapons the crosshair will remained centered no matter what reticle the screen shows. This should be your new center point when using any weapon. Remember, it’s possible to remove and reapply crosshairs multiple times.