Since admins weren't any help and this is the first result on Google, the solution from https://support.reolink.com/hc/en-us/articles/360006240073-Request-for-RTSP-URL:

The format of RTSP address is as below:
rtsp://(user name):(password)@(IP address):554/h264Preview_01_(stream type)
For example, if your camera or NVR has the following information,
IP address: 192.168.10.92
username: admin
password: 111111
then the RTSP URL will be:
Main Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_01_main

Sub Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_01_sub
 
You may also change the channel number to view different channels.

For example, if you want to view channel 2 on NVR, then the RTSP URL will be:
Main Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_02_main

Sub Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_02_sub

Since admins weren't any help and this is the first result on Google, the solution from https://support.reolink.com/hc/en-us/articles/360006240073-Request-for-RTSP-URL:

The format of RTSP address is as below:
rtsp://(user name):(password)@(IP address):554/h264Preview_01_(stream type)
For example, if your camera or NVR has the following information,
IP address: 192.168.10.92
username: admin
password: 111111
then the RTSP URL will be:
Main Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_01_main

Sub Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_01_sub
 
You may also change the channel number to view different channels.

For example, if you want to view channel 2 on NVR, then the RTSP URL will be:
Main Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_02_main

Sub Stream: rtsp://admin:111111@192.168.10.92:554/h264Preview_02_sub