To change the email address in contact form which in on sidebar, kindly edit the sidebar.php file and find
[contactform to_email=”firstname.lastname@example.org” title=”Contact Form”]
and change to_email address.
After looking at your website http://oakstream.tech it seems that it is not showing all the default sections as like in demo ZeroError theme
To show the default home page with all sections
Kindly Go to Settings -> Reading -> Front page displays
click on radio button of Your latest posts
Now Go to Appearance -> Theme Options and click on Restore Defaults in bottom side
Please see the documentation, it will surely help you to customize the theme.
If still getting any problems in customizing the theme or contact form in sidebar, you can send us login details of your site at email@example.com so we can resolve your problem.