Before Apple allows repairs to be started, the device must have Find My disabled. These instructions are for removing a MacBook Pro from Find My but may be applicable to other devices.
You can remove your MacBook Pro from Find My in three ways: from the device itself, from another device on your account, or from the appleid website.
From the Device Itself
Open System Preferences
Select iCloud
Uncheck the box next to Find My Mac. You may have to scroll to find it.
You will be asked for your Apple ID password. Enter that and click Continue.
You're done!
From Another Device on Your Account
(these instructions are for removing your MacBook Pro from your account using your iPhone)
Tap on Settings
At the top you should see your name and a circle with your initials or profile picture. Tap the arrow on the right side.
Scroll to the bottom where you should see a list of devices on your account. Tap the arrow next to the device you want to remove.
Verify that this device's serial number matches the one you want to remove. Then click Remove from Account.
You may be asked to confirm. If so, click Remove.
From the Apple ID Website
On any device, head to your favorite web browser and go to appleid.apple.com. Sign in using your Apple ID email address or phone number. Please note that you may need to use another device on your account for two-factor authentication during this process.
In the menu on the left, select Devices. Then select the device you wish to remove.
Verify that this device's serial number matches the one you want to remove. Then click Remove from account.
Finally, confirm your intention by clicking Remove.
If you are asked for a two-factor authentication code, you will need another device on your account to receive the code.
Assuming you are using your phone, you will see first a message that asks you to make sure you are the one doing the removal. Click Allow.
Then you will receive a verification code to type in to the website.