-allowignoremodconflicts -ignorelaunchmodconflicts
You don't need to find the command line argument anywhere.
What you have to do, is create a text (.txt) file in your mod launcher's directory, and call it "CommandLine.txt"
Once you do that, edit the file and type in "-allowignoremodconflicts", like so:
Now, just save your file and reload the mod launcher (if already running):
I hope this helps!
-allowignoremodconflicts