Add cresc. molto

A crescendo goes from whatever the dynamic level is before to whatever dynamic level you place after.

Select the notes/measures you want the crescendo to crescend over. Add a crescendo line to those notes. Add the dynamic level you want to reach to the note immediately after the end of the crescendo line. Select the crescendo and click the Properties tab (upper left). Open the "Text" tab and add the molto to the Beginning text. If you want, you can hide the line (in the crescendo properties and/or the ending dymanic (in its own properties).

See the attached example.