I want my twitch chat bot to respond to a specific user with a specific reply

Chat and IRC
4

I am not sure what you are asking.

You code shows that if the message is hi you @ the user that wrote hi with the message @username peepoHey

This looks like TMI.js and based on your OP you want

client.on('message', (channel, tags, message, self) => {
	if(self) return;
        if(message.toLowerCase() === 'hi' && tags.username == 'somename') {
		client.say(channel, `@${tags.username} peepoHey`);
	}
});

I’d usually grab the user-id rather than username but it’s all in the tags