Apple provides a tool called Smart App Banners that automatically prompts users to download or install your app whenever they visit your site from mobile Safari:
To use the Smart App Banner, all you need to do is enter the below line of code in the <HEAD> section of your website:
<meta name="apple-itunes-app" content="app-id=myAppStoreID">
Replace myAppStore ID with your personal Apple Store ID. You can find your App Store ID be either searching for the link here or by going into iTunes and clicking the dropdown menu next to your app and copying the link. The App Store ID is the 9-digit number after the "id" portion of the URL.
KNSTRCT's link to its app is:
This makes its App Store ID:
So the Smart App Banner tag is as follows:
<meta name="apple-itunes-app" content="app-id=87948920">.