As a Premium member, you will see a list of all the likes you have given. This gives you the option of looking at a profile that you have given a like at a later date.
You can find the list as quickly as you can give likes. Open your profile (human symbol in the top left corner), then scroll all the way down and tap on "Your given likes".
If you can't see the list, you can take out a Premium subscription to enjoy this benefit and many others.