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You won't be able to add another admin to your account, you will be the sole admin. What you can do is add subusers.
You may allow your subusers to either View Submissions or Edit Forms. Here's a quick guide on How-to-share-forms-with-a-sub-account-user
The only way to allow others to have admin rights is to share your admin credentials with them (which I won't recommend unless you really need someone to have full access). This in turn will give them access to your account, add new subusers, create/delete forms, etc. Basically, anything you can do now can be done by them.