Hi there, @marinabaytravel. Allow me to share some information and provide assistance in changing your home currency from USD to SGD.

In QuickBooks Online (QBO), we can basically change our Home currency in just a few easy steps. However, if you've turned on the Multicurrency feature, the only way to change the home currency is to delete all your data and start over from scratch just like what one of our supports recommended to you as this action is irreversible.

Refer to the image below to check if your Multicurrency feature is turned on:

With regard to starting over, since we can only move lists from QBO to another QBO or QBDT account, yes, you can consider running invoice-related reports such as the Invoice list report and exporting it to Excel. When you're done setting up a brand new account, you can import those invoices again. I've included this article to help you export your data: Export reports, lists, and other data from QuickBooks Online. 

When ready, follow these steps in deleting your account:

If your account is less than 60 days old. 

Note that purging company data is only applicable to QBO Plus, Essentials, and Advanced. 

1. Log in to your QBO account as a company admin.
2. Change the URL to include /purgecompany. So from https://...qbo.intuit.com/app/homepage, to: https://...qbo.intuit.com/app/purgecompany for example.
3. The next screen will provide a summary of the items to be deleted.
4. Type the word “YES” once the data gets deleted, then click OK.
5. Click Wipe Data once your selections are complete.
6. Once the deletion is complete, you will be rerouted to your home page.

The system deletes all data entered into the company, and you're unable to restore or reverse them.

On the other hand, if it's 60 days old or older, follow these steps to cancel your account. If you use payroll, you should cancel your payroll subscription too. Please note that after the account deletion, we keep your data for one year so you can come back to your previous account if you decided to do so.

When done, you can start a new company by following these steps:

1. Sign up for QuickBooks Online.
2. Enter your user ID and password. You can use the same user ID and password as before.

Moreover, I'll be adding this article that'll help you in adding and deleting multi currencies: Set up and use multicurrency in QuickBooks Online. 

Please know that you can always go back here in the comments if you need further assistance in managing your QuickBooks Online account. It's my priority to make sure you'll get the assistance you need and help you accomplish your tasks. Take care always.