@PLJns 

Hi,

The simplest way would be to reset the RE550 to factory default settings by pressing the Reset button (inside the small hole labeled "Reset") and then set it up again like you did before, with the difference that this time you make the network names identical to those of the "regular Wi-Fi".
 

However, whether the Wi-Fi transition will be seamless or not depends wholly on your client devices (phone, tablet, laptop), because when used as a regular wireless extender the RE550 won't assist with the transition.