Cannot edit URL for Datasource

I clicked on "CONFIGURE" for the datasource on a grid, and inputted an URL, but I needed to change the end of the URL, so I pressed "END" on the keyboard, and a box popped up to ask if I wanted to clear the fields, I said no, and it exited the URL box, so I clicked it again, pressed END, and the box popped up again, it is impossible to edit the URL.