If there is a REST or webservice interface, you could use the mendix methods to connect to them.
Check out the academy, there are some examples how to implement it.
You could use the excel import module from the app store.
https://appstore.home.mendix.com/link/app/72/Mendix/Excel-importer
You can also check out the database replication module.
https://appstore.home.mendix.com/link/app/160/Mendix/Database-replication