Open your profile to edit
On the bar, as it were, that gives you font, color and so on, over to the far right there are TWO icons for youtubes
One is purple ( that's the last icon on the right), the other is a coral color. Just to the left of the purple icon. Click that. Past the link of the youtube in there. Be SURE the youtube is located on your profile before you click that icon, else it will go into the spot where last you typed.
Click " Update Profile".