How to i get my existing Bank account back on Banking tab after it was disconnected using Edit Account info

You'll have to reconnect this bank, ashok6.

If you disconnect an account from online banking, it stays active and available in your Chart of Accounts. The system just stops downloading new transactions.

You can reconnect it to start downloading transactions again.

Here's how to connect:

1. Log in to QuickBooks Online.
2. From the Gear icon, click Chart of Accounts.
3. Look for the checking account to reconnect.
4. Click the drop-down arrow under the ACTION column.
5. Select Connect bank. 

You can use these references for a more detailed process on how to connect your bank and manually upload more than 90 days of transactions.

Feel free to message again if you have other questions.