Did you build this machine, or did you buy it assembled from someone? The reason I ask is that the stepper with the default firmware should have been attached to E0 already. The only reason to move a single extruder over to E1 is if the E0 motor control stepper driver chip has failed. Otherwise it’s a bit of work for no good reason. Having even one of them fail by now would be pretty rare, but not unheard of. Having both fail would point to either inadequate cooling (machine in an enclosure without the control box vented, failed fan, wrong fan firmware, etc.) or possibly inadequate grounding of the rambo board. If it was moved and adjusted in firmware, it may be due to the other extruder port having already failed.
To switch to using E1 if it isn’t already enabled in firmware does require some firmware surgery. Cura can probably do it automatically. if not, it’s going to be in the Configuration.h file for the printer, or you can just flash back to the stock Taz 4 firmware (or the Taz 5 firmware if the machine has been upgraded to a hexagon nozzle) Here are the Kittaz instructions on where everything should have ended up. https://ohai.lulzbot.com/project/ad3648a5-711a-4357-a5bc-2ad5e059ccf7/
It would require more effort to switch the harness over to E1 than it would to just set it up using E0 if nothing was wrong.
If it turns out it is melty, you can source an inexpensive used board from https://itworks3d.com/product-category/parts/3d-printer-electronics/
If you want a brand new one, ordering directly from ultimachine https://ultimachine.com/products/rambo-1-3 is the least expensive option. You can also source them directly from Lulzbot.
If the extruder motor is the only part not working, it’s not likely to be the fuses unfortunately.