When I open my phone it tern off by it self

@bruk64227 try to restart is safe mode and see if it still does that.

1. Press and hold the. Power button. (right edge) until the 'Power off' prompt appears on the screen then release.
2. Touch and hold. Power off.
3. To confirm, tap. Safe mode.
4. once you are in safe mode, make sure that airplane mode is off. Now test your phone and see if it stays on.

If that does not work you may have to try a hard reset. Make sure that you have backed up your files since you will lose those.

If even that does not work, it is time to check the power to your phone and start by replacing the battery, then re-evaluate.

How to Factory Reset Samsung Galaxy A02s

Since iFixit does not yet have a guide for that, use this one

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.