Filed itr against wrong assessment year

Hi, 

While filing my AY 2018 - 19 returns I saw that i have recieved a Demand notice from IT in my online portal. I then realised that I have filed the return of AY 2017 - 2018 against AY 2016 - 17. I was not based in India in AY 2016 - 17 and hence did not have any tax liability. However since I incorrectly entered the AY, my entire tax ( which my company had already deducted from my salary and paid) + a huge fine has been raised as a demand. This is running in several Lakhs. Can you please advise how this can be fixed

Regards

Tanu