You can update the app by following the steps below:
1. Open the Google Play app store.
2. Tap the circular icon at the top right of the screen.
3. Tap "Manage apps & device."
4. Tap "See details" under "Updates available."
5. Update the Mario Kart Tour app.
Try the following if the update button is not displayed:
1. Try again at a different time.
2. Restart your device.
Note: Be careful to not accidentally uninstall the app.
You can also check Google Play's help page.