This probably means you did not uninstall it but rather unpinned it from the start menu. Swipe up from the main screen to find all progams listed. If it is there you can select it and pin it back to the start menu.
If it's not there., just look it up in the store. It will say that you already own this app and that you can reinstall it free of charge...
I uninstalled it. It's not listed under "all apps" and when I go to the store it wants me to pay again. The App is World Atlas by National Geographic and I already paid the $1.99 but the store doesn't seem to know that.
Yes, I haven't changed my account but I did do the free Windows upgrade that was offered a couple of months ago. I think that's when the issue surfaced (so to speak ;-). The OS upgrade was not as transparent as I imagined - a number of my settings required fiddling with.
I've never interfaced very well with Apple computers - they seem overly simplified to the point where usability suffers. I can never figure out how to make changes so it works the way I prefer. I'm afraid this new touch screen Windows is one small step in that direction. It just feels nebulous.
Update: I figured it out. Apparently the Credit Card I had authorized on my MS account had expired and I had not entered the new card number. The MS store had tried to charge my card five times over many days but kept getting denied. Eventually the app stopped working (without telling me it was due to a billing problem) and I uninstalled it and tried to re-install it (unsuccessfully). All this without any notification (by e-mail or otherwise that there was a billing issue).