Getting Subform Fields to Display Top to Bottom

Getting Subform Fields to Display Top to Bottom

I have a form where the fields are all in one column. I want to insert a subform where the fields are stacked in one column as well.

I have built both the form and subform but the subform displays the fields from left to right instead of a stacked column. This will cause a problem displaying the subform correctly on mobile apps.

How can I do this please?'

Here is my form with subform now. As you can see the subform "Follow Up Activity" is displaying the fields left to right. I need them to go top to bottom like they would if it was a regular form.

Any help would be greatly appreciated.