A week 53 in the 2020/21 tax year occurs when your regular pay date for weekly, fortnightly or four weekly paid employees falls on 5 April. The number of days in the tax year doesn't divide into a whole number of tax weeks, so 5 April becomes week 53.
If you do have a week 53, there's nothing that you need to do differently. Simply complete your payroll in the usual way dated 05/04/2021, depending on your normal pay day, before you process your payroll year end.