how do i delete subdomain from plesk

[NaiNy]

plz i want some help regarding deletion of subdomains

am using this command
subdomain.exe --remove testsbdomain -domain agent.com

and also using this command
subdomain.exe -r testsbdomain -domain agent.com

but this command is not working and it gives me that output

An error occured during subdomain removal: Can't recognize option "testsbdomain "

where testsbdomain is already created subdomain