When is the last date to revise er-1 returns

You can go to the aces.gov.in ( which you used the web for filing the return) in that you will be having the option in returns filing, if the window is open for current year and the option of revised return will open. You will be also having modify option sometimes. 

Please check the window of Returns and filed the revised return, if it is still open for your F.Y.( normally the window will close by 6 months of the last date of filing of return ).