How to add organization to a group via API?

Hello,

Is there an API call to add organizations to a group? Basically a programmatic way to do what’s in the screenshot.

I see an endpoint to create a group and one to delete a group. You could delete it and re-create it, but would make more sense if this could be updated programmatically.

I’d like something slightly different. I want to add an organization to an existing group - essentially I want one group to be part of 2 orgs.