Yes, you can downgrade your QuickBooks Online Essentials subscription to QuickBooks Online Simple Start.
Please note that changing your plan will disable certain features, such as bill management and multicurrency. If you opt to downgrade, follow these steps:
Click on the Settings icon.
Select Subscription & Billing.
Click on the QuickBooks plan and click on Downgrade your plan.
Choose the version you want to downgrade to and follow the onscreen prompts.