Number of attempts in JEE Advanced if I repeat my class 12th again

Irrespective of your earlier attempts with your CBSE 12th class qualification, you can again appear for JEE advanced with your new qualification of 12th from NIOS,
The year of passing 12th from NIOS will be considered as your first attempt year and the next year you will get the second which is the final chance.
For example if we pass 12th from NIOS in the year 2023, the first year will be 2023. Irrespective of your appearance the 2023 will be counted as first attempt by default. Then you are allowed to appear one more time in the year 2024. That will be the last chance.

In your case, you want to sit for class twelve from NIOS and clear it in the next year, you will be given two additional chances for clearing your jee advanced in the consecutive years. Your appearance for the said examination after passing your CBSE for class twelve would not be taken account since you are appearing for the same class with the different Board and hence you are entitled to get two additional chances to clear your Advanced papers in the next two consecutive years.
As for illustration, in your case, suppose you clear NIOS Board in the year 2023, this would be reckoned as the first year of your attempt and by the way, you could not clear the same in the same year, you can try it in 2024 to clear your Advanced paper.
In that way, you are getting two chances to clear your IIT. Please note that there should not be any discontinuity on your part in maintaining this sequence.