If you've previously opted out of the scheme, taken a payment holiday or are paying in less than the minimum contributions, re-enrolment is a reminder to start or continue saving at least a minimum amount into your pension pot.
Your employer is required to enrol you again every three years if you're still eligible and either not a member of their pension scheme or not contributing at least the minimum amount.
So, if you've been here before then it's likely you're being re-enrolled into the scheme.
Being re-enrolled does not affect your right to opt out.
As long as you have considered the implications of leaving your employer's pension scheme, you can opt out here.