1. Make a copy of your User.ini
2. Open your User.ini
3. Find the [Engine.Input] section and write "altfire" at the key you want to bind to AltFire.
E=altfire
For example
4. Replace Aliases[18]=(Command="",Alias=None) With Aliases[18]=(Command="Button bAltFire | AltFire",Alias=AltFire)
5. Save your User.ini and remember to replace at both places in your user.ini file at the top and the buttom basicly this means you will add this information in twice just scroll down and find it.