Back to the original question...
RTOW is the lowest of TOW encompassing limits such as MLW, MTOW and MZFW.
The limit in an EFB application can be found by calculating the takeoff/landing performance without entering the landing weight, which gives you MLW using existing conditions (those you selected such as airport/runway/temperature/qhn/...).
In essence the EFB allows you to calculate DISPATCH Landing Weight and MRTOW.
What EFB are you using?