Hi Sriram,

It seems every case are different and few having static values.

In that case, Create a onChange client script on Company.

       In script , call Script Include, based on selected company , add all required user <sys_id> in  array result and pass it to client.

    Set that value in user variable.

Note: do not add hardcoded user. instead of that put sys_id of user in sys_properties. Use that sys_properties from script include.