If you have a Paid account, you can enable Co-host features at https://zoom.us/profile/setting. You will then be able to assign a co-host in your Meetings or Webinar, once they are started.
You cannot have Co-Hosts on free or Basic account - and you cannot assign Co-hosts in advance.
Also on a Paid account, you can assign an Alternative host. This can be done in advance - but both the Host and the Alternative host need to be licensed users on the same Zoom account.
But either way - a Meeting can only have one actual Host at any one time. The Host can have multiple Co-Hosts.
Hope this helps.