Use APKPure App
Get 썸네일추출기 썸네일만들기 old version APK for Android
It is a simple but powerful thumbnail extractor. You can select and extract only one thumbnail you want through the video cover.
✔ Thumbnail extraction guide
① Select the video you want to extract thumbnails.
② While viewing the video cover, select a thumbnail you want.
③ Click Save Thumbnail at the top of the screen.