IT Return E-Verification and Revision

Dear Sir,

I've submitted my IT return on 31st Aug 2019 for the FY 2018-19

I've not E-verified it yet.

Also, I've made a mistake in the return and hence, need to revise it for this.

Now my doubt is:

1. Should I first E-Verify the IT Return that I submitted on 31st Aug 2019, and then revise it ?

OR Should I revise the IT Return (Excel file) and then E-verify it ?

Also, what is the last date for E-verification/ Revision of the IT - return ?

Please suggest.