If the FR945 is not listed under the compatible devices for the watch face, you need to message the developer and ask them to make it compatible. I have been using the Countdown! watchface on my 935 and Fenix 5+ and it was not compatible with the 945. I messaged the developer yesterday and he fixed it the same day. Just go to the watchface in the Connect IQ store. On the right hand side of the screen under "Additional Information" there will be a link to Contact Developer.
If it's a CIQ watchface, it might be already available in the app store. If not, use "contact developer" to ask about availability. If it's a native watchfaces (came with the watch) no. That's in the device firmware.
