On AARP site there is an additional $1300 if we claim standard deduction for 65+ yrs old How do I get that?

All you do is enter your correct birthdates and it automatically computes your standard deduction.

This deduction is not exclusive to AARP.  It is a federal deduction based on the Income Tax Law.  The standard deduction for 2020 is $12,400 for singles and $24,800 for married joint filers. There is also an “additional standard deduction,” for older taxpayers and those who are blind. A married filer who is blind or aged 65 and over can claim $1,300 for themselves.

Just be aware that you must be at least age 65 as of 12/31/2020.