Because Microsoft does not officially support direct conversion of Windows 8.1 Evaluation to a full edition via DISM commands (unlike Windows Server), you must use a registry workaround.
Key Management Services (KMS) client activation and product keys How to activate windows 8.1 enterprise evaluation build 9600
your computer. This resets the evaluation timer (usually for another 90 days) and can typically be done up to 3 times. Permanent Activation (Full Version Only) or potentially malware.
If your trial is ending, you can legally extend it (rearm) to gain more time without a full activation: Open the as an Administrator. How to activate windows 8.1 enterprise evaluation build 9600
It cannot be legally “activated” as a full, permanent edition without a legitimate Enterprise volume license. Any tool or script claiming to bypass activation is likely a crack, KMS emulator, or potentially malware.