How can I detect and locate the third party apps using the App Store or the accessories and other devices causing a conflict and issues with me how do I contact the vendor

I was lead to believe that it was new when I purchased it from the Merchant on a matter of a dispute resolution resolving an issue of customer experience, misconduct and mistreatment, It has crossed my mind many times that it could have been a returned device prior to giving it to me, because of all the issues I notice and experience on my iPhone, and no the seller did not set up anything on my iPhone before leaving the store, I did receive a notification way later from seller to schedule a appointment to setup device and that it was a must, but to me it was working just fine at that time and I had told the associate that when I called the merchant, and she insisted that I need to come in,In my mind I was like a whole month later you contact me to tell me this, and didn’t respond to it .