You are supposed to fill and sign the declaration form to and then endorse it.
Normally the declaration form for tertiary institution contain a place where another person apart from the applicant can sign to testify that all the information provided is accurate. Some forms even go to the extent of requesting for stamp as a form of endorsement. So mostly people like pastors can sign and stamp your declaration form to endorse it or any other respected persons in your community. I have not personally seen the forms myself but check to see if there is a place where a witness or any other signature provided apart from yours. The passport you used were scanned and uploaded so you don't have to do anything to it otherwise write your name at the back and sign that one also.