No, you do not not need to re-apply in order for the updates on the PPP loan forgiveness to apply to you. This new legislation applies to all business owners, regardless of when you received your PPP loan.
The amount that you are eligible for also does not change. The maximum amount allowed is still 2.5 times your average monthly payroll prior to February 15th.
The main purpose of the PPP Flexibility act is to make it easier for you to obtain forgiveness by easing the requirements in the original version of the bill.