It depends a bit on which app you mean, but on mobile you can swipe to the bottom to find the 'edit' button and find either an x to remove tiles or a + to add them.
In the Win10 app you can click on the pen/edit in the top right menu to get the option to add or remove tiles.
Hope this helps
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@ThatGreen nice suggestion! Keep it up.
Welcome aboard @Kat.358! By what you are describing it sounds like your tracker might have gone unpaired during the process of deleting the app. Please check if your tracker has been unpaired. If it has been unpaired, please follow these steps to pair your tracker once more. Hope this helps. Let me know if your tiles appear again.
Looking forward to your new comments! 
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