NPM and NTA are integrated in the sense that you first have to add the interface in NPM in order to receive the flow data in NTA. So,
you can either add that interface to Orion NPM:
Go to Manage Nodes > Click on Cisco ASA > List Resources it should then have that interface listed and select it and submit.
You can disable Flow Monitoring from Unmanaged Interfaces, but please read pages 70 and 71 in the Solarwinds NTA Admin guide before doing so. I went ahead and copied and pasted some notes from those pages for you:
Note: Disabling the option to monitor flows from unmanaged interfaces may
significantly decrease the processing load on both your NTA server and your
Orion database server, but it will also decrease the amount of flow data stored in
your Orion database
In a nutshell, if this option is enabled, NTA will save the flow data from unmanaged interfaces and then when you add that particular interface to NPM, it will have historical Netflow data to display in NTA. So if you opt to add that interface on your ASA to NPM, you will have historical data.
Go to NTA Settings > uncheck Allow Monitoring of Flows from Unmanaged Interfaces