There are a few apps that help visualise Service Design projects:
Smaply: create customer journeys, personas and stakeholder maps
Custellence: create customer journeys
UXpressia: create customer journey maps, personas and impact maps
Most of these apps are focused on:
the customer journey: how the service feels to the user
or the Service Design Blueprint of a Service: what is needed for the service to work and all the steps that the customer goes through
More apps for Service Design
Back in the days I collected a list of apps that can help Service Designers.