How can i edit the command in CommandEvent 1.15.2

So i made this code (in 1.15.2):

@Mod.EventBusSubscriber
public class Events {
    @SubscribeEvent
    public static void CommandEvent(CommandEvent event) {
        String cmd = event.getParseResults().getReader().getString();
        cmd.replace("%value%", "example");
    }
}

But i cant find how i can edit the command itself before it gets executed.

I can't use ChatEvent because i also want to edit the commands from a command block,

thanks for the help.