This is in the bottom right of the screen

Ensure each lead has a good trace

You can then tap Capture 12 Lead from the bottom menu

Optional - Print Report

Once the ECG is saved, you can show the automated analysis including the QTc

An automated analysis of the 12 lead, including QTc

You can also go to QT Analysis which will show a specific window and allow continuous monitoring

This view shows a more detailed analysis and realtime monitoring of the QT and QTc