If you have access to the loads for multiple airlines, you can add up to three additional airlines for which you'll see open load requests.
To do so, open the StaffTraveler app or point your browser to StaffTraveler for web. Tab or click your profile picture in the top-right corner of the app and choose Profile & settings. Scroll down to the section Additional airlines. Here, you can add the extra airlines that you can provide loads for.