@RRGT19 

Hello，

Did you want to connect the TL-WA855RE to your new router? 

If so, please put the TL-WA855RE and your new router in the same room, then try to reset and reconfigure the range extender:

How to reset: Use a pin to press and hold the reset button for more than 8 seconds to reset the TL-WA855RE to its factory default settings. If you can see all the lights flashing, then go off and some lights go back on slowly, which means the device has been reset successfully.

How to configure: https://www.tp-link.com/en/support/faq/1373/

If you want to set the same network name with your new router, you can create it at Step 5.

Note: The password of TL-WA855RE must be the same with your new router.

May it help and have a nice day.