You can assign throttle to a switch or whatever you like. This is not a Spirit topic. This happens inside your Jeti.
And of course, you have to tell your FBL which channel of your receiver is allocated to which control input. This is the same for all FBL on the market, as long as your are working with individual receivers.
For Spirit, it is so easy. Just open Channel Tab and select the correct channels for every input. If something is swapped - swap it back
But, the default setting in Spirit and Jeti should perfectly match for the first 6 channels.