As long as your old phone is running Android 6.0 or above, the app will work just fine.
To get started, you'll need to set up your new OnePlus phone, and install the OnePlus Switch app on both phones and approve the various permissions requested by the app.
On your new OnePlus phone, select New Device, select the device type (OnePlus or Android) and follow the prompts. Eventually, a QR code will show up on your display.
Next, on the old device tap Start to prompt the app to launch a QR code scanner and point the camera at your new OnePlus phone.
Last, decide which data you want to transfer. Currently, the app supports transferring the following:
- Call logs
- Applications (without saved data)
- Other files
When you've selected all you want to transfer, select Begin Migration. It's a good idea to have both devices plugged in. During a test run of transferring some apps and pictures, amounting to roughly 6.5GB of data, the OnePlus Switch app estimated it would take about an hour to get the job done.
OnePlus notes that it's working on adding support for older Android devices, more services such as saved app data, and iOS devices.