I linked bank account, but bank transactions are not loading. how do we update the cash cash equivalent with transactions from 3 months back?

Let's add your bank transactions to your QuickBooks Online account, accounts.

You can add those by downloading the transactions from your online banking account and import/upload it to your QBO account.

Here's how to prepare your bank transactions:

1. Go to your online banking account and download your transactions.
2. Check the format and size of your file, it should be a CSV, QBO, QFX or in QBO format. Then, the maximum file size is 350 KB.
3. Once your file is ready, you can now start uploading or importing it. 

Let's now add this to your account:

1. From the left tab, select Banking menu and go to Banking tab.
2. Choose the bank account where you want to upload the transactions into, then click the Update drop-down menu and select File upload. 
3. Hit on Browse and locate the file you’ve downloaded from your bank and hit Open. Then, click on Next to proceed.
4. On the page that appears, click QuickBooks Account drop-down menu and select the account you want to upload the transactions into, then select Next. 
5. Match the columns on the file with the banking fields in QuickBooks, then select Next.
6. Click on Let's go to let QuickBooks add the transactions to your account.

See this manually upload transactions into QuickBooks Online article for more information. 

From here, you can now match and categorise the transactions and then reconcile accounts to ensure your books are accurate and don't have any duplicate transactions.