MikroTik Powershell API

Hello everyone, so im using Sapien Powershell Studio to send commands to my mikrotik. Currently I just create users/password for tool user-manager. To do that i send this commands :
Send-Mikrotik -Connection $C -Command (“/tool/user-manager/user/add”) -Attribute “username=$username”, “password=$password”, “customer=admin”…
$C = my IP adress / user / password
And now my problem is how I can check if a user exist already ? what kind of commands should I send ?