How do I add an extra step to an in-progress dossier?

There are two ways of adding a step to an in-progress dossier.

Add an optional activity. Optional activities can be defined in the process template for the path concerned. You add the activity by selecting it at the bottom left of the dossier.
Use the button at the top right of the dossier and then select ‘New activity’. Select the required activity type, give the activity a name and allocate it to one or more roles.

The activity can now be seen in the dossier and can be used by people whose roles are the ones the activity has been allocated to.