Changing the site URL (& doing it wrong)

Hi there –

I’ve created a sub-domain: https://dev.dreamasreality.com of my main website: https://dreamasreality.com

I now wish to have people visit the main website yet view the sub-domain files which are a totally different design.

I’ve played about (for hours) with the wp-config.php file and the functions.php with no luck, it seems I’m unable to make the switch.

Help, please!!! (BTW I’ve already read the codex and it hasn’t helped me – please simplify for a php noob).