Extract the encrypted code from the obfuscated file (it should be inside a bytes string as the third argument to __pyarmor__). Write this as raw data to a file, say 'enc.bin'.
Run unpyarmor unpack enc.bin pytransform.key out.pyc, where out.pyc is a pyc file where the decrypted code will be written.
Use a python decompiler to decompile the decrypted pyc file, e.g. decompyle3 out.pyc or uncompyle6 out.pyc.