Hi @Lks2019 and welcome to the support forum! 
From what i understand, you get an error message saying that a system process has stopped, am I correct? And if so, does this error message show up during a specific kind of use or does it appear randomly?
One thing that you can try is to reboot your phone in safe mode to see if you receive the same error message there. All apps downloaded from Play store is temporarily deactivated while in safe mode and by doing this, you can see whether this error message is caused by a downloaded app or not. For more information on safe mode and how to use it, click here.
If the same error message appears in safe mode, I would suggest that you try to repair the software using Xperia Companion and a computer. Do note that a software repair will erase all user data from the phone, so it is advised to do a backup before the repair to avoid data loss.
I hope that helped!
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