Full instructions from the manufacturer can be found here.

The basic steps are:

  1. From a laptop or PC (connected on the same network) open a browser window and put in the IP address of your printer. You can find the IP address of your printer by performing a self-print.
  2. Log in with credentials (usually username is root, password is public)
  3. Go to System Configuration
  4. ENABLE #9100 Multi Session
  5. Click Submit
  6. Click Save (on the left)
  7. Opt for the first option and click on Execute

The self-print that occurs after the restart will show Multi Session enabled.