Previewing an Op Template
When using the template picker, after searching or browsing for your Op you'll see a symbol of a mobile phone next to the Op name/description. Click this to open a preview.
NOTE: You can only amend templates after you've selected them.
Previewing an Op as you Build / Edit it
Whilst using the Op editor, you can access a preview on the left side of the screen. The vertical bars (highlighted in the image below) can be clicked on to expand/collapse the Preview and Details sections - which is useful if you're working on a smaller screen.