Welcome to the Community. I'm here to provide information on how you can correct the beginning balance of your account in QuickBooks Online.
You need to check if the account was reconciled before by checking the ending date field that shows the last statement ending date. We'll need to fix the balance depending on the scenario of your situation.
Let's try following the steps outlined in the article below:
In case you need quick help with the beginning balance, you can also reach out to our Phone Support Team. They'll be able to check your account and perform additional troubleshooting to correct the amount.
Here's how you can reach them:
I'm a post away if you need further help with the reconciliation. You can reach back to the Community team by leaving a comment below.