Cut LED strip into two same length pieces (depends on various placements on the balance scooter)

Solder 3 thin jumper wires to the beginning of each strip (be careful to choose the right end (look for a tiny arrow on the strip)

Prolong wires on one strip because they will have to go through the center tube of a balance scooter (30 cm or so will be enough)

Push long wires through the middle tube of a balance scooter (assuming you opened it) and connect +5V, GND and data wires of two strips in parallel. Glue the strip into place. Solder +5V, GND and data wires to the Arduino (for data I used pin 6).

Solder two wires to Arduino's 5V in and GND and solder other ends to balance scooter's sensor board's free pads (any two free pads that give you voltage of 5V and GND)

Upload your code to the Arduino

Perform cable management, insulate the Arduino, glue it into place with hot glue (make USB accessible for further software changes). Make sure everything works, close your balance scooter and enjoy.