Thanks for your reply.
Unfortunately, my html code is 3 columns same as the template from the beginning.
When I added “viewport-fit=cover” to the <meta name=””>,
I was able to make it 3 columns on iPhone X landscape mode.
Template:
<meta name=”viewport” content=”width=device-width, initial-scale=1, maximum-scale=1″>
After customization:
<meta name=”viewport” content=”width=device-width, initial-scale=1, maximum-scale=1, viewport-fit=cover”>