i have a new lowrance hds-5x and i have a split screen with fish finder on left and gps/nav on right. i need to zoom in on navigation on right as it does me no good under its current viewing mode. it shows almost 1/2 of the state of california. how do i zoom in to show the exact river i am in and closer detail? thanks for any help. i've gone through the owners manual and can not find a solution.