Your first and simplest action to try is turn it off. If it's frozen, disconnect the USB-C cable connector from the port on the back panel of the instrument. This usually helps.
Unit still crashing? Try this: connect your SD card to your computer and delete the hidden “Workspace” folder.
But if your device lost power during the upgrade, the SD file structure was damaged, or the firmware doesn’t boot up for any other reason, you can perform one of the two emergency flashing procedures which are described in another post of this knowledge base.