You can find this option by going to:
Header & Footer section
Under Footer, add a Form Footer
Alternatively, you can set Form Footer Source to Airtable Field and define the field that contains the description under Form Footer Field. This way, each record can show a different description.
The contents of the Form Footer (Field) will show up above the Submit button on your form.
💡Note
The form footer will only appear on the last page when the multi-page mode is turned on.