There are several ways to find your Beats serial number:
Wear your Beats and make sure they’re connected to your iPhone, iPad or Mac.
Do one of the following:
iPhone or iPad: Go to Settings 
, then tap the name of your Beats near the top of the screen.
Mac: Choose Apple menu 
For Beats Fit Pro, Powerbeats Pro 2, Beats Solo Buds or Beats Studio Buds +, the displayed serial number is specific to the charging case. Tap the serial number to display the serial number specific to the left earbud; tap again to display the serial number specific to the right earbud.
Before you begin, make sure you’ve added your device to the Beats app for Android.
Wear your Beats, then make sure they’re connected to your Android device.
Go to the Beats app 
For Beats Fit Pro, Powerbeats Pro 2, Beats Solo Buds or Beats Studio Buds +, the displayed serial number is specific to the charging case. Tap the serial number to display the serial number specific to the left earbud; tap again to display the serial number specific to the right earbud.
Tip: The serial number and other printed information on Beats is very small. You can use your iPhone like a magnifying glass to zoom in on text. See Use iPhone like a magnifying glass in the iPhone User Guide.
Beats Fit Pro or Powerbeats Pro 2: Look for the serial number on the inside of the charging case.
Beats Flex: Look for the serial number on the right control module.
Beats Pill: Look for the serial number on the bottom of your speaker.
Beats Solo 4 or Beats Studio Pro: Expand your headband and look for the serial number on the slider above the right ear cup.
Beats Solo Buds: Look for the serial number on the inside of the charging case. If you have a transparent case, look for the serial number on the bottom of the case.
Beats Studio Buds +: Look for the serial number on the inside of the charging case. If you have the transparent case, look for the serial number on the back of the case.
On Beats Fit Pro, Powerbeats Pro 2, Beats Solo Buds or Beats Studio Buds +, the left and right earbuds also have a specific serial number.
Note: You can also find your Beats serial number near the barcode on the original packaging, or on the original product receipt or invoice.