To create an accelerando/ritardando, proceed as follows:
Procedure
Select the notes and select “Accelerando” from the Group/Ungroup submenu.
A dialog appears.
Use the radio buttons to select the desired combination, that is, define whether you want an accelerando or a ritardando and specify the desired note values and click OK.
Double-clicking on the “Grouping” text opens the Grouping dialog, allowing you to select another combination.