Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I may be helped in answering your question adequately and correctly, by knowing what model of Floscan you have.
But if your Floscan is a model 7000 series, for instance, then I have to say that there may be no way to connect it to your Garmin device. It is not listed as having an interface (e.g. NMEA type) to any other device, just as being engine mounted or engine-connected (as is, obviously, necessary).
The Garmin device you have, is pretty capable of displaying engine data. But: does it have NMEA connectors or ports on it? other than NMEA, it has Bluetooth and WiFi connectibility capability... it can do Bluetooth and WiFi to other devices... but, the Floscan (model 7000) apparently has no such capability.
You would need a Floscan - or some other vaguely similar device - with NMEA or with WiFi or Bluetooth interfacing capability, to connect the tachometer/fuel-meter/etc. to the Garmin device.
Let me know what model of Floscan you have. Or what you might need further in the way of advice for this question. Thanks.