Ah okay, I understand.
You probably have a database, unrelated to Rasa, with a list of employees, no? You can query the database to look for the name of the employee (from JavaScript you can do so with Ajax or Axios).
Or, if’s too much of a hassle querying a database from JavaScript (which it is), since you’re getting the employee ID and using it as sender ID, I guess you’re doing that by getting it from the interface. Isn’t there a way to do the same for the name? If not, isn’t it possible to add a hidden HTML element containing the required data?
Then, after getting that info, you can pass it as an entity in your payload.
Again, can’t you just query the employee database from your Rasa custom action?