ASP.Net MVC Not able to load one of our web site in IFrame

I am facing a issue that i am not able to load a site in IFRAME. i have two web site one is main web site another web site load main web site in IFrame. both web site developed using ASP.Net MVC5.

Few months back main site used to load in IFrame of another web site. these two web site hosted in IIS of same server. suddenly TLS version was updated in that server but i am not sure that this issue is occurring for TLS version update. two web site use https.

When i am running a site which load another site in IFrame then i saw chrome throwing error in console tab of developers tool. here i am sharing the screen shot of those error.

i search google and found some guide line that few people said this is cross origin error or X-Frame-Options related error.

so to handle this situation i plug in below code in Global.asax file of web site which will load in iframe of another site. here is the sample code which i used but no luck.

protected void Application_PreSendRequestHeaders(object sender, EventArgs e)
{
    HttpContext.Current.Response.Headers.Remove("X-Frame-Options");
    HttpContext.Current.Response.AppendHeader("Access-Control-Allow-Origin", "*");
}

Some people saying to add below code

protected void Application_Start()
{
//Bundles and stuff are here
AntiForgeryConfig.SuppressXFrameOptionsHeader = true;
}

please tell me in which project i need to add above code ?

please see my error screen shot and help me with sample code that how to get rid of this situation. Thanks