I will be happy to help you out. It is possible that there is something plugged up inside the diswasher causing the no spin on the lower spray arm. First I would remove the spray arm and inspect the holes. Look for anything visible blocking any of the holes. From there I would remove the internal parts directly under the spray arm.
Here is a diagram below. Number 14 is what ultimately propels the water through the system. If this is worn or damaged, or plugged up with food particles then this may be your issue. As far as removing the parts.
You will need to be patient and pay attention to the order you remove the pieces. In general it is easy to disassemble. If you don't have the correct order putting it back together it may get frustrating. Also if the screen (number 6) is filled with water deposits this will also slow down the water flow.
Here is the diagram. If you have anymore questions please feel free to ask.
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