from tnzapi import TNZAPI

client = TNZAPI(
    Sender="YOUR_EMAIL_ADDRESS",      # API Username
    APIKey="YOUR_API_KEY",            # API Key
)

request = client.Set.Reschedule(
    MessageID="ID123456"              # MessageID generated from system OR your message ID if specified
    SendTime="2020-05-12 12:00:00"    # New Date/Time
)

response = request.SendRequest()

print(repr(response))