Shortcodes for custom form fields

I’m loving Ultimate Member plugin, it’s powerful yet easy to use and I’m starting to use more advanced features. I want to know how to get a shortcode for a custom field. I added an extra field called ‘device’ in the login form, I want to use that for an external url like other shortcodes. For example I have a page with an external link https://form.jotformpro.com/form/000000000000?yourName%5Bfirst%5D=%5Buser_firstname%5D&yourName%5Blast%5D=%5Buser_lastname%5D – I want to append this custom ‘device’ field with a shortcode, so I would be adding something like &device=[device]. I can’t find the syntax for this. Please could someone assist?