Hi Marianne
You can't change the beginning of a fiscal year! Only the end of one (which then carries over to the next year).
FY17 ended Sep 2017 - there is no getting around that. So it sounds like what you want to do is to have a short fiscal year that consists of one month - October 2017. Then the next FY will be a full year ending October 2018.
Before you ask your Adagio consultant to do anything, you will want to confirm this with your "real" accountant.
If the above is true, you really have your hands tied, because changing a fiscal year retro-actively is a very very difficult thing to do in Adagio.
Steve