First you want click on 'My Friend Codes' under the 'My ACC' section to your left under the animal crossing community logo. From there you should see 'My Wifi Games and Settings' in a blue bar and it should say edit next to it. This will open a new page and down the list will be 'Nintendo 3ds' and there is a space to enter your friend code and next to it-check the box under the 'In Registry' column Then scroll down to the very bottom and hit submit. That should get your code up and running
I hope this helps!
Signature--------------
Tell me how I did, leave me a rating~!
You did it! Now you have a blue wifi button next to your screen name like I do! In future trades you want to hit the blue wifi button to request a friend code so you can get the code to enter into your ds. Sometimes the other player will hit the blue button first and you have to go under the 'my friend codes' section to accept their request. Once two players have their fcr (friend code requests) in order they can see each other's friend codes in the 'my friend codes section'
Signature--------------
Tell me how I did, leave me a rating~!
I'll add you and then you can go through and see how to accept a friend request. Under 'my friend codes' there is a 'friend code requests section' and there you can hit a box next to a username and then 'hit accept all checked' above the username section. Then we should both be able to see each other's friend codes under 'my friend codes'
Signature--------------
Tell me how I did, leave me a rating~!
You did it! Now all you have to do is register a friend in your 3ds under internet and then once both of us enter the codes we will be able to visit each other's towns
Signature--------------
Tell me how I did, leave me a rating~!