Question: how to transfer data from oneplus 3 to one plus 6?
Answer: Step 1: Fetch the OnePlus Switch app. Head over to the Settings on your OnePlus 6 and scroll down to find Advanced. Open the OnePlus Switch tab to launch the service. ... 
Step 2: Using OnePlus Switch to transfer data. On your OnePlus 6, open the OnePlus Switch service and tap on “I'm new phone”.