Financial year 2017-18

You Cant File AY 2018-19 Income Tax Returns now Except Notice from It dept

How to ammend mistake made in return then?

No way for amend/revise the ITR for FY 17-18...
In case You got any notice from dept then You must be rectify the same..

Can I request rectification u/s 154 to correct mistake as to avoid any Hassel in future.?

154 is possible only after ITR is assessed. And under this you can not add fresh income (left out income)

Time being you have to carry that tension or voluntarily write a letter to AO to brief these facts and put it on record. And leave the ball in AO's court.

In future this will at least save you from penalty proceedings.