For visit visa extension you need to visit the health center before 30 days after your arrival and complete the medical tests(blood and Xray) and once the report is done(normally 4 working days) you need to visit the immigration department in gharafa and you can decide between 1 - 5 months(max6 months)for extension.

But i don't understand why you went to Airport immigration for extension or is it a tourist visa you have which is only 28 days,