Unfortunately the Garmin Connect app does not integrate with Google Fit, and therefore your fitness data from your Garmin device cannot be automatically imported into Spire. You of course can always manually input your data into Spire, learn how HERE.
Garmin has indicated that they have intentions to add support for Google Fit integration, so definitely give them a shout and let them know you want it. https://support.garmin.com/en-US/
If your have a Garmin tracker that syncs with the Garmin Connect app, then you can set your fitness data to automatically update in Spire. To do this the Garmin Connect app needs to be set to send its data into Apple Health, which shares data with Spire. While Garmin makes some of the best fitness bands on the market, their app can be a bit finicky. So getting it set up to share data with Apple Health (and Spire) takes a few extra steps compared to other devices. But good news! We have outlined all of those steps for you, with pictures!
The goal is to get the Garmin Connect app to share data with Apple Health, and then to prioritize that fitness data in Apple Health.
Here are the steps:
1) Go into the Health App on your iPhone:
2) From the bottom menu bar select "Sources":
3) Tap the Garmin "Connect" App logo
4) Either "Turn On All Categories" or at least ensure "Steps" is set to On.
*Also be sure you have done the same for the Spire app. More on that HERE.
5) Now on the bottom menu tap "Health Data" then the big "Activity" block in the top left
6) Tap into the "Steps" Section
7) Tap "Data Sources & Access" (this is different then the "Sources" section from the bottom menu)
8) Tap "Edit" in the top right
9) Tap and hold on the three lines icon that appears next to the "Connect" icon and drag it to the top of the list under "Data Sources"
Now ensure your Garmin device is synced to the Connect app. The Connect app should now forward all of your steps data into Apple Health and Spire will be able to pull that data into the Spire app.
Note* The Garmin Connect app doesn't not immediately send its data over to Apple Health, to seems to do so periodically. You may be able to force this update to Apple Health (and ultimately then Spire) by closing out of the Garmin Connect app and relaunching it.