Once your company is past its first year, it’s no longer possible to change the Fiscal Start date field
Workaround:
How do I export and import company records from one company file to another?
Exporting and importing customer records using CSV format with Sage 50-Canadian Edition
Exporting and importing vendor data using CSV format using Microsoft Excel
Exporting and importing employees data using CSV format
Exporting and importing inventory and services data using CSV format
Exporting and importing account data using CSV format
Exporting and importing Projects data using CSV format with Sage 50-Canadian Edition
Exporting and importing price lists using CSV format in Sage 50