How can I have my Mii wear hats?

In Find Mii on the 3DS, you can win various hats that you can apparently put on your Mii.

I tried going to the Mii Maker to see if that was where I could use the hats but I didn't see an option there.

How do I put the hats that I have won on my Mii?

Solution 1:

It's not in the Mii Maker, which is kind of counterintuitive:

The special Mii hats can only be used in StreetPass Mii Plaza. The "Mii Settings" that you're looking for are not present in Mii Maker. Select your Mii in the StreetPass Mii Plaza and you'll see "Mii Settings", where there is an option to wear a hat that you found in Find Mii.