Sub label

hello,
I want to ask if can I change the sub label in name field for example,
If I can’t, is there anyway to make a field with same name field format.
I don’t know if you get my idea.

but for example,
I want to ask my user for label dimensions
and I want the question be like this:
Dimensions:
Length:—- Width:—–

The page I need help with: [log in to see the link]