It appears that .pkz and .pkt files are both used by Packet Tracer software from Cisco, however, a conversion or transformation of data seems not likely. At best you can import and work with the .pkz files in the program, run some simulation and export .pkt file, but that's about it.
Convert Cisco Packet Tracer archive to Packet Tracer network simulation file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert pkz to pkt on Windows
An interactive teaching and learning tool
Convert from pkz file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.