Adding appsettings from app.config to web.config after publishing

I have solution with 2 projects and web application.
And my appsettings are added in app.config which is present in one of the project.
And then I published the webapplication.

But when i deploy the published folder in the test server, the appsettings are missing and that need to be added which I read from internet...And when I try to add my appsettings in the web.config(Published Web.config),and run the application, I am getting 500 server Internal error

app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<applicationSettings>
.......
</applicationSettings>
</configuration>

web.config:
<?xml version="1.0"?>
<configuration>
  <configSections>
    <section name="error1" type="test, test1, Version=1.0.1.3, Culture=neutral, PublicKeyToken=77d9ae8727c9ec66"/>
    <section name="error2" type="test2,test3, Version=1.0.0.0, Culture=neutral, PublicKeyToken=77d9ae8727c9ec66"/>
  </configSections>

"If i add app setting here I am getting error"
<applicationSettings>
.......
</applicationSettings>
</configuration>


Can you please help me with this?