We recommend that you search the forum before posting questions and, IF you can't find a suitable answer, then post it.
If you have access to your database (either via PHPMyAdmin - PHP Web interface for MySQL, or PGAdmin - PHP Web Interface for PostgreSQL, or command line) use the INSERT command detailed in this post
Change the user_id for the one you wish to provide full Admin Access.
You may consider, in this type of situation, to register a group email account for the Admin, instead of single-person account or creating multiple Admins.
Although more people will read the messages, at least one person will receive it, read it and take action.
It's up to you to decide the best practices in this case.