Your plan will be fine. You’ll be in Terminal 1 with Asiana so when you land follow signs for Transit. Once you pass through transit security you go up an escalator to the main terminal area. At the top of that escalator you will see a small podium with the transit tour info. You can sign up for the tour of your choice then head to the lounge. Or you can head to the lounge then come back to the podium to sign up. But it’s best to sign up early as some tours fill up.