Hello Caroline,
Thanks for reaching out to us!
Unfortunately, there is no direct way to adjust the order of custom fields in Filter Bar at the moment other than put them in alphabetical order. It may very well be possible with some custom development, but I do not have a workaround that is supported by the plugin.
I’m sorry for the news, but I hope this at least helps answer your question about the possibility of changing the order of filters.
Let me know if you have any other questions and I’d be happy to help as much possible.
Best,
Brendan