QB Issue Resolution:

You can change the financial year by going to the cog in the top right/account and settings//advanced/accounting. If you want to run a report with an extended financial year you can.

Resolution for Issue 'Financial Year. Our company was incorporated in August 17 and we have extended our financial year extended to December 2018. How can I change this in Quickbooks?' available: Yes (Solved).
Source: Intuit Community forum.

Financial Year. Our company was incorporated in August 17 and we have extended our financial year extended to December 2018. How can I change this in Quickbooks?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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