wp network meta update 1 site_admins exampleuser

This overwrote the entire entry and set it only to “exampleuser“. I believe I did not pass the value, exampleuser, correctly. Previously when I ran

wp network meta get 1 site_admins

The return value was in this format:

array (
  0 => 'username1',
  0 => 'username2',
)

I feel I can fix this problem if I know how to format the entry correctly

wp network meta update 1 site_admins exampleuser

What do I need to use for the –format parameter?
How to I enter the site admin into the site_admin network meta table?

$super_admins =array( exampleuser' );