A strange question, how to change the function of the "alt" key

[sdgmlj]

When using the box selection tool, the official explanation is as follows:
Which function is executed during normal box selection (without pressing any key)
Which function is executed when holding down the alt key
So I wrote the mod in the official format, which is normal for me and most players
But some players have reported that holding down alt is ineffective, while others have reported that holding down shift is only effective
It can be confirmed that his alt key function has been changed. Strangely, I couldn't find how to change this key in the game's key settings
So what I want to ask is, where can I change the function of the alt key?