Howdy Shearwater2002,
It sounds like you want to remove your old MacBook Pro from Find My Mac, but you no longer have access to the device. The article linked below will walk you through the process of removing the device from iCloud.
iCloud: Remove your device from Find My iPhone
Remove an iOS device you no longer have
If you no longer have the iOS device because you gave it away or sold it, you need to remotely erase it before you can remove it.
- Sign in to icloud.com/#find with your Apple ID (the one you use with iCloud).
If you’re using another iCloud app, click the app’s name at the top of the iCloud.com window, then click Find My iPhone.
- Click All Devices, then select the device.
- Click Erase [device], then enter your Apple ID password. Because the device isn’t lost, don’t enter a phone number or message.
If the device is offline, the remote erase begins the next time it’s online. You’ll receive an email when the device is erased.
- When the device is erased, click Remove from Account.
All your content is erased and someone else can now activate the device.
I hope this helps,
-Jason