I omitted/missed answering/giving information to one of the field on the form.

[scott833]

1) I omitted/missed answering/giving information to one of the field on the form, therefore it was returned to me.
2) I forgot to fill in one of the field on the form.

 

[Barb_D]

... one of the fields, plural.

I would say 2.

Or, "I accidentally left one of the fields blank."

 

[Rover_KE]

I wouldn't use fields at all. I'd say spaces.

Rover