How do I downgrade to simple start plan from plus plan (with multi-currencies function)?

There's no way to downgrade your plan. You can purchase a third-party service to migrate your data to a new QBO account as a workaround

Hi there, @c2alliance.sg.

Downgrading from the QuickBooks Online (QBO) Plus plan to the Simple Start plan is unavailable if your Multicurrency feature is enabled, as it can't be turned off once activated. This feature changes the financial tracking structure permanently, locking out the ability to downgrade.

As a workaround, you can cancel your subscription and create a new account. Before cancelling, export all essential data from your current account, including reports, customer and vendor lists, the Chart of Accounts, and invoices, to safeguard your records and prepare for reimporting into the new account.

Next, cancel your existing QuickBooks subscription. Here’s how:  

1. Go to the Gear icon.

2. Select Subscription & Billing.
3. Click Cancel.
4. Select Continue to cancel.

Once done, visit the QuickBooks website and subscribe to the Simple Start plan.

During setup, configure your account to meet your plan's needs, and import the exported data into the new subscription.

Feel free to utilize the Reply button below if there's anything else we can assist you with.