In the Search menu click on Valley on Screen. This moves the data cursor to the lowest waveform valley displayed on the screen in a selected channel.
OR
Double-click the right mouse button anywhere in the bottom annotation line. This will also move the cursor to the lowest valley displayed on the screen in a selected channel.
Choose Search Valley on Screen (ALT, S, S). This also moves the cursor to the lowest waveform valley displayed on the screen in a selected channel.