What should I do when client transfer his STP to us?

Hi there, 

I am an accountant , one of my client used Reckon mobile app to do stp by himself from July 2019 to March 2020. However, he wanted us to do his stp from April 2020. 

So, 1. Should I set up a new account for him in Reckon One?
       2. What should I do before lodge his april wages to ato? What should I do to match the YTD amount ?
       3. Will it be double lodged?

Hope hear from you guys soon. Thank you in advance.