Have not signed my completed return and it hasn’t been submitted and I want to add another amount to my deductions which the app isn’t allowing me to do ?

As long as you have not filed your tax return, you can revisit any section to make changes using the topic search feature in TurboTax Online. On the left-hand side go to Tax Tools>Tools >Topic Search or Topic List. Then type the section or form that you need to update in the search box and click Go.