Normally hosts look for cohosts with extensive experience of hosting themselves. So the best way to become a cohost is to start as a host yourself. Once you are a superhost you can register on the Airbnb platform as a cohost to offer your services to local hosts. @Daniela2545
Yes you can set up your own marketing channels to promote your cohosting services and invest in advertising to promote your services to hosts in your area @Daniela2545
My advice was just that hosts are more likely to use the services of cohosts who are experienced hosts.