Joining the partner program is accomplished through a pull request to opensearch-project/project-website in the
_partners folder. The suggested method is to fork the repo, add the partner markdown file and build the website locally to verify it looks correct then contribute the changed file back to opensearch-project/project-website.
Alternately, this form will help you make the pull request and properly sign the DCO in the GitHub web interface by creating the pull request for you. You will need to have a GitHub account and be logged in for this form to work properly. Due to limitations in this process, you will need to add your logo through another method like GitHub Desktop or command-line Git.
This visual guide can help you understand how a partner tile connects to the rendered HTML.