LORIOT runs the LoRaWAN network server and the connectivity; Cloud Studio IoT gives that data a place to live. The link is an application output in LORIOT that points at your platform instance with an access token, so the devices you already operate start feeding dashboards, alarms and reports.
Log in to LORIOT and create an application for the devices you want to send over, or use an existing one.
In Applications > Output, add the Cloud Studio output with your instance name and an access token created for this integration.
Create each device in Cloud Studio IoT with the same address it has in LORIOT, and pick its model so the payload is decoded.