How to Clear the Cookies and Cache on a Mobile Phone

iOS - Safari

1. Open the "Settings" App, and navigate to the "Apps" section.
2. Find and select "Safari."
3. Tap the "Clear History and Website Data" button.

Apple Support: Delete your Safari history, cache, and cookies on iPhone. 

Android - Google Chrome

1. Open "Chrome."
2. On the right of the Search Bar, Tap the Kebab Button ( ⁝ ) to display an Action Menu.
3. Tap the "Delete browsing data" Button.

Google Account Help: Clear cache & cookies.