Su to another user to run script

I have a script ( the name is /tmp/script1) , the content is simple , just copy a file to another directory .
Now I would like every user will change to a specific user ( eg. userA ) before run this script so that the script will be run by userA , that mean I want only userA run this script , I tried make the below change , but it do not work , can advise what can I do ? thanks
$vi newscript
su - userA
/tmp/script1

man sudo , it will help for your request.

You might like to use

sudo -u username