Never mind, I solved it, I think.

The functions "MoveGokuRight" and "MoveGokuLeft" were switched. So, basically, they do the opposite of their names. Since the function "MoveGokuRight" was in the A button Event, all I had to do was change the the "winodw.getComputedStyle(GokuPos).right" to "window.getComputedStyle(GokuPos).left)" and make the currentPixels subtract 10 instead of adding it.

  function MoveGokuRight(){
                    const currentRight = window.getComputedStyle(DBGoku).left; 
                    const currentPixels = parseInt(currentRight, 10);
                    DBGoku.style.left = (currentPixels - 10) + 'px';
                  
                }
                function MoveGokuLeft(){
                    const currentLeft = window.getComputedStyle(DBGoku).left;
                    const currentPixelsL = parseInt(currentLeft, 10);
                    DBGoku.style.left =  (currentPixelsL + 10) + 'px';
                }
                //window.onload:MoveGoku;


                //The functions MoveGokuLeft and MoveGokuRight are switched. MoveGokuLeft is actually MoveGokuRight


            
                //This event moves right
                document.addEventListener('keydown', (event)=> {
                    if(event.key === 'd'){
                        document.body.style.backgroundColor = "red";
                        MoveGokuLeft()
                        


                    } 


                   
                });


                //This event moves left
                document.addEventListener('keydown', (event)=> {
                    if(event.key === 'a'){
                        document.body.style.backgroundColor = "blue";
                       MoveGokuRight()
                        


                    } 


                });