If this is a live stream, you should be able to set these details in the encoder, or through the IP camera interface. If you do not have access to these details then you would need to use the Transcoder.
The GOP/keyframe interval is set at the source. Wowza can do this within the Transcoder as it is essentially acting as an encoder. If Wowza is ingesting the stream then the keyframes need to be set within the external encoder.