this is very simple if the pump feed is by a simple silicon hose in the top of the water tank.
Get yourself a veterinary syringe with end large enough to fit neatly into the feed hose. Fill the syringe with water, start the machine pumping and plunge the syringe into the line.
CAREFUL not to plunge the syringe too forcefully or you can blow the other end of the feed line off the pump...then you have to pull the body to get to the pump to push the feedline back on.
The above should "unseize" the thing and it should pump through. Stop the pump, put all back together and.....whalla.
This is not uncommonm and is very easily remedied in most cases as above.
If on the other hand the water feed is through a valve in the bottom of the tank you may well have to pull the body so you can get to the feedline to the pump, and the rest is still as above.