I mistakenly answered a question that my wife owner capital gains while filling out return. How can i go back and correct it?

Go back into the income section for  that income and edit. You will be able to go through the list of questions again. On a joint return in should not make a difference in tax owed.

I'll try to find it. Thanks

Your question is not clear. Please indicate whether you have filed your or your wife's return yet.