Adding Tax Collected at Source (TCS) is currently unavailable in QuickBooks Online. Meanwhile, I recommend that you consult with your accountant. They can provide some alternative ways for entering TCS into the system.
We also have hundreds of apps that provide a wide range of services. You might want to look for an app that allows you to add TCS.
Here's how:
Go to the Apps menu, then proceed to the Find Apps tab.
Select the dropdown list for Browser Category.
Click a category.
For future reference, check out the following articles below for some guidance in tracking taxes in QuickBooks Online: