Connecting your Rocket League Steam Account to your Challengermode Account is quite simple, it won't take more than a couple of minutes.
If you go to any Rocket League tournament without having a Rocket League Account Connected, you will find a Connect Steam button located at the upper right side of the Tournament Overview page.
Click this button to connect your Rocket League Steam Account.
After clicking the button a Connect Steam Account window will appear.
Feel free to read through this information at your own leisure - to proceed with the process, click the Sign in through STEAM button located at the bottom.
By clicking this button you will be re-directed to Steam (https://steamcommunity.com/...)
Once here you will be required to enter your Steam Username and your Password to sign in to your Steam Account.
After signing in your Rocket League Steam Account will be connected to your Challengermode Account.
If the process goes through, you will once again be re-directed back to Challengermode where the following window will appear - but with your Steam Account rather than the one in the example.
You will also be able to see Rocket League under the sub-menu Your Games on the left hand side of Challengermode.
Now that you have connected your Rocket League account, you will be able to join Rocket League tournaments!
Running into other issues, or do you have additional questions? Feel free to chat with us by clicking (?) on Challengermode.