How can I restore admin capabilities?

The string below actually represents an array in serialized form.

a:1:{s:13:"administrator";s:1:"1";}

Here:
a:1 means an array with a single element
s:13 means string and the length of the string followed by

Array 
{
     "administrator" => "1"
}

Once that is in the table, you can use the unserialize() function to return it to an array for use in your code.

Many thanks.