1) Go to Configuration Files from your game panel.
2) Select clientpermissions.xml
3) Click the "Text Editor" from the right side. (don't forget to select Save & Exit)
Follow this format as an example:
<?xml version="1.0" encoding="utf-8"?>
<ClientPermissions>
<Client
name="Example"
steamid="xxxxxxxxxxxxxxx" <<<< (You will use your steamID64 here)
permissions="ConsoleCommands, ServerLog, ManageSettings">
<command
name="heal" />
<command
name="spawn" />
</Client>
</ClientPermissions>
This is how it looks like:
<?xml version="1.0" encoding="utf-8"?>
<ClientPermissions>
<Client
name="Your_name"
steamid="12345678987654321"
permissions="ConsoleCommands, ServerLog, ManageSettings">
<command
name="heal" />
<command
name="spawn" />
</Client>
</ClientPermissions>
4) Restart the server