Hello @Cristina ,
Microsoft doesn't have a direct support email address you can write to. Everything goes through their online ticketing system.
If you’re using the keyboard wirelessly:
Go to Settings > Bluetooth & devices. Then hold the Esc key on the keyboard for about 5 seconds. The LED should start blinking, which means it’s ready to pair.
If you’re trying to register the keyboard but can’t find it under the normal Surface device options:
Go to account.microsoft.com/devices and sign in.
Click Register device and, when it asks for the device category, choose Microsoft Accessory instead of Surface PC/Tablet.
You’ll need the keyboard’s serial number. It should be a 12-digit number and can usually be found on the fabric spine or hinge of the keyboard, on the original box, or in the Surface app under Device Information.
If none of that works, you can also call Microsoft Support directly. The number depends on your country, so use the support number for your region rather than calling a random number you find online. You can find your region's number here: https://support.microsoft.com/en-us/support/
Best regards,
Dimitrios