Thanks for taking your time to contact PUBG support!
I see that you wish to know how to add friends on your steam friends list. As per your concern I’d like to let you know that you can add your Steam friends by clicking on Add Friends button in the friend info window or the link below.
[Add friend link}
If you can not search for your ID on Friend Finder, go to your friend's profile page
You can add friends.
If it is not possible to add a friend on your profile page, your target may be in the "Profile private" state.
Profile can not be added to profile when private. "
Hope this information for helpful for you. We’re always available here to assist our Survivors, Please let us know if you’ve any other question or concerns so that I can assist you accordingly.
See you in Battle ground!