There's a little arrow in the upper left corner of my screen does anyone know how to take it off?
Red and green arrows? That's from volte and can be disabled in the phone app settings, however it only disables volte it doesn't get rid of the arrows. Volte is voice over lte and let's you make higher quality calls using lte. It's not really a necessary feature because a lot of phones don't support it so if you call someone and they don't have volte it won't really do anything. For some carriers it let's you use data while on calls but tmo let's you do that already anyway.
If it's not that arrow attach a screenshot and I can let you know what it is.