This subject has been extensively addressed.
Add the XVR to Blue Iris by its IP address and login credentials just like you would add a camera. Camera channel 1 will be added by default. You may want to try 'Find/Inspect' with just the IP address and login credentials to obtain the correct stream information vs. selecting a brand. BI is pretty good at figuring that out.
You then add the additional analog cameras by again using the XVR IP address and credentials but using the next desired camera channel number accordingly.
The camera channel number should be specified in the main and sub stream address information, not in the Cam# box which may or may not properly reflect the correct channel in the stream info. If 'Find/Inspect' was successful, the streams for all channels should be listed in their respective Stream Profile drop down boxes.
Once the analog cameras are added, they'll become their own entities in BI apart from the XVR and can be independently configured.