Depending on your situation, you can transfer your account with any of the following methods:
If you can use LINE on your previous device before changing to a new device
On your previous device, start LINE and go to Settings > Account transfer > and turn ON the Allow account transfer setting. Afterwards, tap Continue on the "How to finish transferring your account" screen that will appear on your new smartphone.
If you can receive text messages on the phone number you registered to LINE
From the “How to finish transferring your account” screen, tap Get account transfer code. You will receive a text message to the phone number you registered on LINE. On your new smartphone, enter the account transfer code from the text message that was sent to you.
If you are using the PC version of LINE
From the “How to finish transferring your account” screen, tap Get account transfer code. An account transfer code will be sent to you in a chat message on LINE. After checking the message with the account transfer code, enter it on your new smartphone.