How to tame!

Cosmo is a passive tame, put chitin in your zero slot. (An easy source is glow bugs) After feeding a piece, Cosmo will run off and start a game of red-light/green-light. When Cosmo glows bright white (green), run towards him to try to feed him another piece of chitin. If he glows red, stop moving. If you move while he is glowing red, he will web you and run off. The taming percentage drops fast, so you need to reach him as fast as possible. It reminds me of Squid Game! I recommend clearing the area before taming, even of passive dinos because his webbing will agro creatures.

TLDR;

Chitin in 0 slot

Feed cosmo

Do not move when cosmo glows red.

When bright run up and feed again.

Repeat as fast as you can for higher tames