In some cases, the app does not work completely as intended. Think of, for example, repeated crashes, or a crashing app. In this case, you can then clear the app's temporary storage to essentially start it over with a clean slate. In the first instance, it is useful to check whether you have the latest version.

Check version

You can find this via App info > Advanced > at the bottom. (App info can be found by holding your finger on the app for a second) Via Advanced > App details you can go to the Store to check if there is a new version.

Clear storage

If this does not solve the problem, the app may need to be cleaned. In that case, I recommend that you empty the app's storage.

You can find this via App info > Storage space > Clear storage.