Every three years you must assess if employees need to go back onto a pension scheme. Your re-enrolment duties vary depending on whether you have any employees who fall into a worker category that you must re-enrol.
You can find out more about re-enrolment and redeclaration from The Pensions Regulator.
Let's run through the four main stages of re-enrolment.

You may want to align your re-enrolment date with other key dates in your business or to avoid any seasonal peaks which may result in an influx of new members.
If you have a single pay frequency, consider selecting a re-enrolment date that aligns with the first day of a pay reference period to avoid pro-rata pension contributions.
On your re-enrolment date, you must assess employees who you've previously assessed for automatic enrolment and who have:
You must re-enrol employees who:
You can also choose whether or not to include employees who are eligible, but who've left your automatic enrolment pension scheme less than 12 months before your re-enrolment date.
Next you must write to any employees that you re-enrol, within six weeks of your re-enrolment date.
Finally, you need to tell The Pensions Regulator (TPR) how you've met your legal duties for re-enrolment by completing an online re-declaration of compliance.
You must do this within five months of the third anniversary of your duties start date or staging date. Go to thepensionsregulator.Gov.UK to find out more.
If you use the Pensions Module to carry process your workplace pension scheme, you can use it to help you carry out your re-enrolment duties. How do I process pension re-enrolment with the Pensions Module?
If you aren't subscribed to the Pensions Module and re enrolment is due, you need to carry it out manually. Process Cyclical Re-enrolment without the Pensions Module.