To export your data from Propertybase you will need to be the Administrator. Go to Setup / Data Management / Export Data. There are two options available. 'Export' and 'Schedule Export'. The 'Export' button is to export data immediately, while the 'Schedule Export' button is to export data in a future date and can be scheduled to happen multiple times.
Once you have decided with which option you would like to export with, you are able to choose whether you want to export all the data out over propertybase or just a few Objects.
For further instruction you can go to the Salesforce article on Exporting Backup Data