YAM has special built in support for the Genesis TCP/IP stack by being able to query the currently active username. So it supports to automatically start YAM with the user that your Genesis TCP/IP stack is currently running. E.g. If you have Genesis configured for a user "john doe" and you have the very same username in YAM configured, it will startup automatically with that user enabled and doesn't query for any user selection or password.

However, if for some reasons you are not able to sync the user names of Genesis<>YAM, you can start YAM either from the command line with the option "USER <USERNAME>" or by adding the 'USER' tooltype to the YAM icon. In that case, YAM will then automatically select the specified user and just query for the password.