Word VBA - Expand a header if a certain checkbox is ticked?

Used VB for Excel, but new to VB for Word. I'm not sure how to expand a header if a certain checkbox is marked true.

ActiveDocument.FormFields("Check1").CheckBox.Value = True

I got that snippet straight from Microsoft Document and dropped it in a If statement and still get an error. Then, I don't know how to reference a specific header and execute the expand. All I have there is Collapse/Expand all headers.