How to set up GST ITC and GST as a specific number not a rate?

Hi Vicky, 

Thank you for reaching out on this. 

If you have complex GST enabled you should be able to see input tax tax code in your rate setting with your GST centre. 

While you will be able to track a specific number, not a rate for ITC, Quickbooks Online currently not supporting the ability to include that as part of your BAS. You can run a "Transactions by tax code" report to see transactions with the ITC tax code. 

Hope this helps and please let us know if you have any questions.