I have upgraded all my computers and now getting an error, The serial number is already in use by the maximum allowed computers. How can i reset this if i don't have access to the old devices

I need help, I have upgraded all my computers and now getting an error, The serial number xxxxxxx is already in use by the maximum allowed computers. You need to deactivate another computer within 30 days to use this product. How can i reset this if i don't have access to the old devices