I do not have a navigation button in my apps list. How do I get to it and turn it on?

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It is driving me crazy!! If I go over the speed limit or the car's perceived speed limit, a loud voice that I cannot figure out how to turn off, says, "the speed limit is 25 miles per hour", or something like that. How can I get to the navigation system to turn this off if I don't have a navigation icon in my apps? I bought this car used and love it except for this one feature. Thank you.