@WiktoriaKościel,
The username and password should be those of the user who you're trying to get a token to act on behalf of. In other words, if I had a Digital Worker that was going to request a delegated token to act on behalf of John Doe, the process would need to be given John Doe's username and password.
PS - I would
strongly suggest removing, or at least editing, that attachment so you're not showing people your Tenant ID, Client ID, and Client Secret.
Cheers,
Eric