Was tricky for me too.
1º: Make sure the folder 'KSM_Add_Voice' is inside data folder, like any other mod.
2º: Inside KSM_Add_Voice there is a folder called 'sounds'. open it and check the voices. choose your favorite.
3º: You must copy the name of the one you chose. For this example I'll choose and copy 'voice_AsahinaYuno'. Note that the thing copied is the same name of the folders inside 'sounds folder'.
4º: In the game folder go to 'data' , '_base', and open 'unitdatas_recruits.json'.
5º: Find the line "voiceAndDialogues" and change the default to the name u chose. In my example it will be ( "voiceAndDialogues": "voice_AsahinaYuno", ).
Code is a pain so only change the default for voice_AsahinaYuno. Careful to not change anything else. This will make every women in the game to have the voice pack you chose.
Somewhere there is a file that takes care of every custom character in the game, finding this file and changing the default to the voice pack you chose also works for them. Sadly I forgot where it is, as I hardly play with custom characters.
For those who dont know what we are talking about:
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Its a mod that lets you change voices in the game.