How to reset the Sled:
https://supportcommunity.zebra.com/s/article/Resetting-the-RFD8500-RFID-Sled?language=en_US
Update firmware:
Use the 123Scan Configuration tool from zebra.
To connect the sled I had to remove the current version and install the new 64bit version. When it is connected the green light in the back is on.
https://www.zebra.com/us/en/support-downloads/rfid/rfid-handhelds/rfd-8500.html