The GP607 does not have a dedicated microphone input, so it is not possible to connect a microphone directly.
However, depending on your setup, you may be able to use a microphone by connecting it to a device such as a mixer or mic preamp that has a mic input and a line output. You can then connect the line output from that device to the GP607’s Input jack.
Note that the Input jack is a stereo mini jack designed for line-level signals.
If your microphone is mono, be sure the connected device outputs a stereo signal or uses a mono-to-stereo adapter to ensure proper input.