stick with desktop if it works, online will be more expensive and doesn't have Forms mode and only good for 1 return.
if it's yellow with "Needs Review" then click Review on the existing 1099 to edit it. If it's white and doesn't need review you can click the dropdown arrow to expand that item and that will show Edit button. You can also go into Forms mode and edit the 1099 worksheet directly.
Unfortunately there is no way to turn it off asking about import when you add new investment, just click Skip Import at the bottom of that screen.
I have found the navigation to sometimes have an inconsistent flow through Investment Income Summary list and import etc, but generally to add a new 1099 you should able to click Add Investments (at the bottom of the list), then Skip Import, select 1099-INT (or other type) and you should get the interview input screens.
If you get stuck you can return to Wage & Income by clicking the tab at the top, "I'll Choose What I Work On" then click Visit All in the Interest and Dividends section, or Update on the 1099-INT line item etc, and that should bring you back to the Investment Income Summary list.
