You cannot add it on your own. You may list them in your GS profile. The Google Scholar automatically adds them. It is like Scimago Profile for Scholars, you cannot do it on your own.
Select the "Add articles" option from the menu. Search for your articles using titles, keywords, or your name. Your citation metrics will update immediately to account for the articles you added. If your search doesn't find the right article, click "Add article manually".
Hello! I would like to connect with you to expand my research network. It would be great to exchange knowledge and collaborate on potential projects in the future. Let me know if you're interested in connecting, and I look forward to hearing from you!