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Antonio, I'm guessing that you mean the washer pump isn't working and you want to replace that. Not sure if a 77 is the same but on my 78 there is 1 screw holding the filler neck and 2 screws holding the washer bottle (tank). The rear one of these 2 screws isn't all that easy to get to though, you might need to remove the splash shield at the bottom of the fender.
Removal of the tank/pump assy would require some additional engine disassembly but it's not required. The washer pump on a '77 can be replaced without removing the tank from its general position in the engine compartment. It just needs to be unbolted so it can be shifted around a little to enable pump replacement. All the bolts can be reached with a little patience. RockAuto has replacement pumps cheap.