Accessing custom log in for Mail from mobile device redirecting to zoho default log in page

Accessing custom log in for Mail from mobile device redirecting to zoho default log in page

How do I change this in my settings so that when I access my company's website mail log a mobile device, it shows my logo log in and not the default Zoho log in (this doesn't happen when I access it from my desktop).

You all are always a lot of help!

Thank you,

Stephen