Check the Navigator you get at check in at the port. It will list where & when to do that. I'm not trying to be difficult, but it can vary from cruise to cruise.
There will definitely be a particular place listed for the first day. After the first day though, you can go to guest services to try for more/other tastings. Or to cancel!
In our Navigator from June on the Fantasy, it said to go to La Piazza. However, they were clearly booking somewhere else too because the bartender started out saying he had room for 5 people at a Mixology tasting and then he was only able to complete 2 of them... We were able to talk to the bartender and squeeze in one more person, but 2 people missed out.
I can relate! As our PAT arrival time is 10:30 on 8/5 for our Dream sailing. Since everyone in our party is now 21, I booked a few tastings through the app, but will see what else there is to offer.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!