QB Issue Resolution:

Once you turn on multi-currency you cannot change your home currency.

If your account is less than 60 days old, you CAN purge your data and start all over.  Here is the article on that,

https://community.intuit.com/articles/1282054-how-do-i-delete-all-my-data-and-start-over-from-scratc…

Resolution for Issue 'How to change my home currency after turning on multi-currency' available: Yes (Solved).
Source: Intuit Community forum.

How to change my home currency after turning on multi-currency: 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.

Support for CAN purge
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Error Recovery for CAN purge [Canada]
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