If a person clear KVPY while doing graduation 1st year Can he join iiser next year with Scholarship

Yes if you pass your 10+2 on the year of admission or on the previous year then you are eligible to apply.
Now your kvpy scholarship should start from the year on which you are going to take admission.
For example if you are going to take admission on 2020 then you must pass 10+2 on 2020 or on 2019.
And your kvpy scholarship should start from 2020.