It is really easy to add yourself as an admin in your Rust server.
Step 1: Make your way to http://rcon.io
Step 2: Click “Log In” on the top right
Step 3: Enter your server information
The server IP is your server IP
The port is your RCON port, not game port. This is usually 28016, but check first on the game panel.
The RCON Password is the password you were asked to create when making your server.
Step 4: Enter the following command:
“ownerid STEAM64ID "playername" (Replace STEAM64ID with your Steam 64 ID, this can be found at https://steamid.io/ and replace playername with the name of the player
Step 5: Then run “server.writecfg” (This saves the ownerid to the config file)
Step 6: You can add moderators, by replacing the ownerid with moderatorid and following the template
Step 7: You will need to relog to get your owner/moderator tools.
You can add moderators/owners offline, by making your way to:
And either adding moderatorid or ownerid, following the same template as above
A full indepth guide can be found at https://www.corrosionhour.com/add-rust-admins/
Thanks to @SpikyZA for this guide