I managed to do it!
After some more searching I found this link. Which was posted on drones4life.
After it installed, I went to C:\Program Files (x86)\DJI Product\DJI Assistant 2\AppFiles\main.js and removed the two slashes in front of mainWindow.webContents.openDevTools()
Now it worked. The Assistant opened with the debug window.
For anyone else who wants to reprogram this button and stumbles across this topic, I'll include the rest of the steps.
-When DJIA is opened, go to the resources tab within the debug panel and navigate to Local storage>file://
-In the list on the right, change the debug key from 0 to 1
-Connect the Mavic and wait for the icon to show, in my case, it said Mavic Pro despite having an Air connected.
-Open the Air, and click on Parameters in the left menu bar
-Search for "g_config_control_control_mode" (without quotations)
-Change its value from 8 to 3
After I did this, I tried it out, and it works! When I now flip the Sports mode switch, it switches to Atti mode instead, and vice versa.