You must proceed with a one-time sync to keep your existing reading history saved on your account. You can proceed with the sync on the screens shown below.
[ APP ]
1) A pop-up will appear once upon launching the app with instructions on syncing your reading history.
2) Go to Settings > Sync Reading History
[ Mobile Web ]
1) A pop-up will appear upon opening the mobile website with instructions on syncing your reading history.
2) Go to Settings > Account > Sync Reading History
* This feature is available on Android/iOS versions 2.N.N and higher.
* This feature is not available on our PC site.
* Your reading history cannot be restored if you delete the WEBTOON app, delete related app or mobile web data, or change your device.
* If you log out before the sync is complete, parts of your reading history may be lost.