Availment of unavailed ITC of FY 2020-21 in April 2021

Dear experts,

I have some unavailed ITC of 2020-21 as per GSTR 2B.

And I believe that we can avail ITC of any prior period upto filing of return of tax period September of next year.

Also, we can avail ITC in excess of as shown in GSTR 2B only upto 10% of eligible ITC.
Portal does not allow availment of more than 10% of ITC.

So how can I avail ITC of FY 2020-21 in return of April 2021?

Kindly advice.