that’s easy. When you are in your profile, there is a separate link which says ‘Add Certification/Training’. When you click there, you first have a choice of organization through which you are certified, and then a further subcategory of the type of certification. Then you just fill in the fields as required, and save.
It will get into the status ‘pending’ until the organization has verified your certification. Be aware that not all organizations are verification partners in which case I would get on their nerves until they become one :-).
Log into your account. Once you are on your homepage, click the “My Account” tab at the top (next to your name/log out). You should be in your profile. Scroll down to Certification/Training (on mine it is just above “CPR”). There is a blue “Add Certifications/Training” link to click. And you are there.