Are you trying to adjust the line spacing of the text in order to align the text with visible lines already present in the format of the form?
There isn't a text formatting tool in the form section. You need to create the from field and edit the properties to allow Multi Line Scrolling and to Allow Rich Text Formatting. Then exit the Form section by clicking the hand tool. Click in the field and press Ctrl+E to pull up the text formatting tool bar. Click more, then paragraph. On line spacing select Exactly and enter the amount of characters that you need in order for the spacing to apply appropriately.
Hope this helps!