Here's a step by step process to add admins to your youtube channel.
Here's how to add users to your youtube channel.
Change CHannel Owners & Managers Google Resource
Add or remove access to your youtube channel.
If you're trying to add a manager, admin, or someone to help you with comments or SEO, this is the simple way to get them added.
You should know that only Brand Accounts allow for users to be added. Personal Youtube accounts don't have the ability to add users. This might change, but if you can't see these settings, you need to either convert to a brand account OR you need to create a brand account channel.
2 - Hit Settings
3 - Hit Add Users
Step 4 Login
Step 5 - Manage Users and Permissions