Click the [Add Member] button in the member list:

A list of all players who have logged into the server will appear. Click on a player's name to add them as a dominion member:

If there are too many players, making it difficult to find one in the list, click the [SEARCH] button at the top of the list to directly enter the player's game nickname for adding:

Warning

You must enter the exact player's game ID. Fuzzy search is not supported.