I need to re-activate my bank feed and am wondering if it will back date to when it stopped?

Glad to have you hear, ttowntennis. 

You can reconnect your bank feed in QuickBooks Online via standard feed or direct feed. 

If you connect your bank account via standard feed, some banks let you download the last 90 days of transactions. Others can go back as far as 24 months.

However for direct feed connection, after your bank approves your connection, your bank will begin sending your transactions from the approval date forward. No historical transactions will be sent to QuickBooks. You can upload historical transactions manually.

You can follow these steps to connect your bank account: 

1. Go to Transactions tab and select Banking.
2. Click on Link account.
3. Search for the bank account you would like to connect.
4. Select Continue.
5. Enter your bank username and password and follow the onscreen steps to connect. 

For more detailed information, you can check on these articles: 

Connect bank and credit card accounts to QuickBooks Online

Connecting your bank account to QuickBooks via Direct feed FAQ

Feel free to let us know if you need any help. Have a nice day.