Install on Wi-Fi. You do not need to remove your physical SIM.
Before you start
The iPhone should be unlocked and on a recent iOS version. iPhone XR and newer models support eSIM. Confirm your exact model on the compatibility page.
Add the plan
Open Settings, then Cellular or Mobile Service, then Add eSIM. Choose Use QR Code and scan the code from your order.
Name the line with the country, for example Japan, so you can tell it apart from your home line.
Turn it on when you arrive
Set the travel line as your mobile data line. Enable data roaming for that line. Leave your home line on if you still want texts and calls on your usual number.