HRA EXEMPTION WHILE GETTING RFA BY EMPLOYER

I am working with PSB and was receiving RFA instead of HRA by bank for 8 months, after that got transferred anywhere and start getting HRA only for the remaining 4 months in FY 21-22.
Now how can I claim for HRA Exemption?

Should I sum up (Basic+DA) for all 12 months or for only 4 months on calculating exemption amount?

Should I consider that RFA amount and if yes then How?

Please guide on this, and will be very thankful if you guide with some data example.