Open the app and look for a built-in cache clear option in its settings
Go to Settings
Tap General
Tap iPhone Storage
Select the app
Tap Offload App to clear app data used for storage while keeping documents and data
Tap Delete App to remove the app and its data completely
Reinstall the app from the App Store
Sign back into the app if needed
Clear Safari cache by going to Settings
Tap Safari
Tap Clear History and Website Data
Restart the iPhone after clearing cache if needed