A Shopify handle is a text which comes after your domain name as a part of your permalink that is leading to your content
There are 2 ways to set up
Click to Publish page > Set handle or URL > Publish now
Admin Shopify > Online Store > Pages > Choose page for setting handle or URL.
Click to "Edit website SEO"
Set handle > Save
If you have any issues, lets contact our support team for resolve.