@V-Duke
Opening the file in another program by itself wouldn't change anything. Since it sounds like it didn't even opened it at all, shouldn't worry.
If the extension is still a CHKN, try to open the chkn on IMVU Create. Click the "Open a Local Project" button in the middle of the three:

Select your chkn files, one by one. They should open each project (chkn) you have.
After that, if you want to see the project's files, click this button once said project is open:

Tada! Just as Souljah said, chkn are just some kind of zip file that IMVU likes, a way to say it. The actual files inside the product are there in the folder after you click the button from earlier.
Hope it helps.