iFrames are an advanced feature that rely heavily on the website you are inserting being formatted correctly. We generally recommend you only attempt to iFrame sites you control (and can make edits to in order to improve how they look in your Plattar app).
However, if you are iFraming a site you dont control, check if they have a mobile version of the page (the easiest way to do this is to open the site on your device’s browser, then copy the link).