You will have to do the following steps if you want to overwrite the default contact form with a form created by xform.

• Please navigate to X-Form and click the Cog icon of the form you want to overwrite with.

• Now navigates to the Integration tab. Tick the checkbox Enable For Layout Position

• On the Custom CSS section, add the following CSS rules

#information-contact form.form-horizontal {
    display: none;
}
#information-contact h2 {
   display: none;
}

• Click the Save and Continue button to store the changes.
• Now navigate to Design -> Layout, Now edit Contact Layout. Finally, add the Form under the X-Form to the Content Bottom position.

That’s all.