Unable to update GST no.

I'm here to make sure that you'll be able to update your GST no. in QuickBooks Online, sharathjyothsna.

May I know if there's an error message that you've encountered when updating GST number.? This way, we can provide you accurate steps and fixes.
 

Let's log in to your QBO account using a private or incognito browser. Press these shortcut keys on your keyboard to open one:

• Press Ctrl + Shift + N on your keyboard for Google Chrome and Mozilla Firefox. 
• Press Command + Shift + N for Safari. 

Once logged in, try to update GST number again to double-check. Please follow the steps provided below.

Note: Only the admin user can update the GST number.
 

1. Select Taxes at the left side menu.
2. Then click on Edit GST and choose on the drop-down and hit Edit Settings.
3.  Edit the GSTIN and click save.

If this works, it means that you need to clear the browser's cache so the system can start fresh.

Additionally, I've also added this article that'll help you set up GST/VAT rates: Add tax rates in Quickbooks Online.

Tag me in a comment below if you have other questions about taxes. I'll be sure to get back to you. Have a nice day!