How can I change company start date?

You can’t.

There isn't one anywhere in Desktop. It is asked as part of the Interview process, but it isn't stored and controls nothing.

Everything you put in the file, you will put the Date on it.

Only QB Online has a "start date" that prevents specific entries.

so, I'm setting up quickbooks.  after entering my account information, it asks to import my data starting 1/1/20 and i clicked okay.  Then i realized i wanted 2021!  I don't need last year's banking info.  How can i change this?

Welcome to the Community, @pitkrew. I can walk you through clearing old transactions by deleting or voiding each transaction.

Please know that deleting a transaction will remove them completely while voiding a transaction assigns a zero value to the item but retains the transaction details. Here's how: 

Delete Transactions

1. Open QuickBooks, click the Lists in the main menu bar. 
2. Click Chart of Accounts from the drop-down menu. Then, select to open the account that contains the transactions you want to delete. 
3. Scroll to the transaction in the account screen. QuickBooks displays transactions in date order, with the most recent at the top of the screen.
4. Click to select the transaction you want to remove, then click Edit in the main menu. 
5. Click Delete, then OK to confirm that you want to delete the transaction.

You can repeat this procedure for each transaction you want to delete.

Void Transactions

1. Go to the Lists in the main menu. 
2. Select Chart of Accounts.
3. Click to open the account with the transactions you want to void.
4. Select the transaction. Click "Edit" in the main menu and then click Void.
5. Click Save and Close to save the voided transaction.

Repeat this procedure for each transaction you want to void.

Here's an article that can guide you on how to match or add bank transactions in QBDT.

For future reference, read through this article: Reconcile an account in QuickBooks Desktop. It helps you learn about balancing your books by matching your actual bank account statements with QuickBooks. 

Feel free to come by here at any time. I'm always here to guide you more with your banking concerns. 

I just bought QuickBooks and entered the wrong start date. I entered 2021 and needed it to be 1//1/2020. How do I change I bought 2021 QuickBooks desktop pro plus. I would like to go back through the setup wizard. Help!

Let me help you change the start date, @Lauriejo.

You can select the first month of the 2020 fiscal year. It will assign the first day of the month automatically.

Let me guide you through the steps:

1. Click Company.
2. Select My Company.
3. Click the Pencil icon in the COMPANY INFORMATION section.
4. Go to the Report Information tab, then select the first month of your Fiscal Year.

Also, I'll add this article for more insights in creating a new record for accounting in QuickBooks: Enter opening balances for accounts in QuickBooks Desktop. It covers how to handle pending or outstanding payments.

Additionally, you and your accountant will need to complete specific tasks in closing out the year and prepare for this new year. You can check our QuickBooks year-end guide to learn more.

Please let me know if you have other questions in mind. I'm here to help anytime. Have a great day ahead!