So you do this via Flea Market. In the Sell section there's a dropdown menu. At the bottom of that menu it should say Lorwolf (For Stud). Once selected it will pull up all your male wolves that aren't on cooldown. If you have a lot of males it may take awhile for you to dig through the pages to find him, but once selected you can set the stud price and the duration.
Just be mindful that if you pull him out of Stud early he will still have a full cooldown like he was bred. Hope this helps!
Editing: If he's one of your progen/starter wolves, you can't stud him. I just remembered this.
You're welcome! I, admittedly, tried doing the same thing when I first joined. Was a bit sad when I learned that your starter wolves couldn't be studded. xD