Who to fix mobile software

Have you tried visiting local repair stores? (I'm sorry I can't fully understand your question, are you saying where to repair your phone or that the software of your phone isn't working.) I'd also recommend that since you're phone is discontinued that you should avoid going to official Samsung stores as they would most likely propose you get a new phone (assuming that's what you don't want)

Questions to ask yourself:

Has your phone been damaged in its exterior?

Have you installed malicious applications on your phone?

Is your phone updated to the latest update?

How is your phone's storage?

Where did you buy your phone from?

@ojas86589 post a picture of the "coding" you see when you start your phone. It sounds like you may need to reinstall your software. For that I would try a factory reset first. The problem with that is that you will lose all of your pictures/music/contacts/sms/ etc but you do not have access to them the way your phone is right now. Try something like this video.

在已经存在的问题里加入图片

No reason to go to the Samsung store since the phone was made by LG.