Use APKPure App
Get Simple Interval Timer(인터벌타이머, old version APK for Android
Simple Interval Timer(인터벌 타이머, 간격타이머, 운동시계, 권투시계)
It's simple and easy to use.
Frequently used exercise time can be easily used by saving it as a time set.
5 seconds before you start exercising, you can hear the sound or vibration.
Also you can use Korean and English.