Text hidden by a non editable layer

[MsPetaRabit]

Hello,

I'm trying to fill in a PDF that was sent to me however there are sections of the PDF where my text ends up sitting underneath presumably previous text boxes. See image.

I cannot delete or edit (as there are no text boxes etc) the whited out area is. How do I rectify this? 

Thanks!

[MsPetaRabit]

I just wanted to add that the text colour is black before anybody suggests that. 

[Bernd Alheit]

Use Tools > Prepare Form and add a form text field. Then fill the text field.