How to reflash android?

Question

Android

I bought a smartphone for my father, by mistake, apparently, he provided access to the system, a third-party application. Are there any readers who have reflashed android, or reinstalled through a computer. It is important for me to master this business. Resetting the settings did not help, the android also bugs out. I know how to switch to developer mode, this is where the knowledge ends. I want to download the original version of the android that is installed on let's, and then completely clear the hardware and upload the downloaded version there. Please tell me what will help me with this? Either a link to the site, or instructions, you can assume that I do not understand anything about this. That is, I make a desktop, I have not come across gadgets.

Answer 1

https://4pda.to/forum/index.php?act=idx