The controller is located at the bottom of the down tube as shown below:

Please make sure the proper-sized screwdriver is used or you increase the risk of stripping the screws.

Please share pictures of all connections and wires. This will help us determine what the issue is more effectively.

Step 1: Remove your battery from the bike.

Step 2: Remove the screws holding the lower battery compartment panel. 

There are 4 screws to remove from the very bottom.

Step 3: Remove 4 screws from the bottom cap of the bike shown below.

Now that you have accessed both sides, you can carefully pull the wires out of this location. 

Step 4: Inspect the connections 

Start by disconnecting each cable. Once completely disconnected, you can slide the controller up and out of the battery compartment.

Please share pictures of all connections and wires. This will help us determine what the issue may be more effectively.