adobe acrobat standard DC version 2015 cannot be started after changing the computer

We bought 2 sets of adobe acrobat standard DC version 2015, but after the original computer was old and replaced with a new computer, when it started, it showed that the serial number was already used by another computer, and it could not be reauthorized to start. The original computer had been logged out and removed. The condition of the new computer is still the same. After asking the original manufacturer, I found that the serial number has been activated 4 times, but it cannot be reset. How can I troubleshoot it?