How can I resolve the CORS issue when loading a website into an iframe?

i am actually working with a client for creating a webview mobile app and when i try to load the website into iframe, i get the CORS issue. So how can I load my website into Iframe?

And if we can set CORS headers on the external resource, to say you allow it to be loaded from another domain and adjust the content type then, I can set Cors headers to be set on my own domain which is used by shopify store. So how exactly I can modify headers on shopify?