Given the nature of how Corsizio works, generally speaking there is no need for you to import old data from a previous service or similar source into your Corsizio account, but this will all depend on the kind of data you are interested in, which will be outlined below.
Previous Event & Attendee Data
Corsizio is meant to be used to manage events and registrations, not customers or client relations. It is an event-centric service, which means that everything revolves around events. Therefore, if you want to add a previous event attendee, there is no place to put them, unless you add them to a certain event. Of course, you can re-create any old event(s) you had and add to them the attendees who registered for those events, but this will be a lot of work for you and ultimately does not help you in any way to use Corsizio unless you want to use Corsizio’s reports for your past event data. However, it may still not reflect all data perfectly depending on the transactions associated with those past registrations.
Going forward, the assumption is that any new attendees will be registering themselves to your events, with the odd one being manually added in by you.
Current Event & Attendee Data
If you have current events that you are still accepting registrations for and would like to change over from another service to using Corsizio, then you will need to create those events in Corsizio (you can use the clone feature for similar events) and add any registrations that you may have received elsewhere manually to that event. There is no way to bulk import events or attendees/registrations as each registration service out there is configured to work in different ways, and transactions cannot be moved between different services.