Old version outlook app the html and CSS not rendering properly design was broken unwanted lines are showing, But latest new outlook app properly rendered, how to resolve the issue?

Question

Our clients are use old version outlook app we have designed FTL template using html and CSS, The Design properly works in outlook web email and Gmail and all other emails but old Outlook App design was broken, unwanted lines are showing many CSS property not working,
Note: Same thing working fine in new Outlook App.

Please help me how to resolve the design issues in old outlook app.