This would depend on if it was for Auto enrolment or not and if the new scheme is taking over from an existing scheme.

Hi Yes its for autoenrollment. Client didnt set up a scheme in time. Now have a scheme set up. The payroll started Sept 2017

You will need to find out when they should of started their auto enrolment duties and may possibly have to work out contributions manually or reprocess.

This article may help
ask.sage.co.uk/.../std_adp.php

And if you can, I would personally recommend the 1-2-1 auto enrolment sessions. They will be able to guide you through the process but have a read of the article first.

The Staging date was Feb 2018. The employees have been assessed through nest would this be ok ?

If the employees have been assessed and have had all the relevant correspondence then you will be able to process via payroll using the option of "I have assessed my employees manually using another system" this will then ask when they were auto enrolled and when the correspondence was sent out. you can then manually calculate how much the pension would be from that time.

If the employees have not been notified then you will be best to contact TPR for next steps then the Sage helpline 0845 111 5555.
Hope this helps