In order to initiate a movement, you first need a personal base. This base does not have to be large, but its participants should be aware of their task and become active for the cause - each according to their possibilities and abilities. The point is to find such people. They would be the first members and companions on the path to United Mankind.
There are many places all over the world where you can find these companions. You could do it like the international Registry of World Citizens. But that would be too much bureaucracy to start with. Also, the benefits of world citizen ID cards are disproportionate to the effort required for them.
Perhaps the simplest method could be to look for companions on social networks on the Internet. I have started a trial on Facebook. Anyone who is interested can join the side United Mankind Pioneers.
See also the article at Substack: Is mankind worth it?