The forms mode is not intended for direct data input except in rare circumstances of some unsupported calculations. Doing so, in place of the interview mode, voids the TurboTax accuracy guarantee because many forms are linked to other forms that the interview mode automatically does. It is up to the user to know what forms link to other forms when using the forms mode.
Many form entries are not direct entries but calculated results from other forms and/or worksheets.
The forms mode is intended more as a trouble shooting tool or a tool to view the forms.
What is it that you are trying to enter?