How Can I restore to stock image ??

Hello, I have a Sprint HTC One M9. I just have unlocked it with help from @stifilz (Thank you!)

He has asked me to Downgrade to 5.0 with Bad Boyz V1.1 Since the phone is S-ON and had version 5.1

Everything was fine, I Downgraded the version to 5.0 and he Unlocked successfully my phone. However I experienced an issue. it started powering off by itself everytime when the phone goes standby. He told me.. it's because that I have a 5.1 kernel on 5.0.2 rom that's the reason.

Indeed, when I installed the latest version of Bad Boyz which is 2.6.651.11 ( 5.1 ) the issue gone. However, I experienced another issue: it keeps telling me an error after the boot finishes: "Unfortunately, the process com.google.process.gapps has stopped"
I click OK, but it keeps showing all the time

Now, I want to restore it to stock image of 5.0.2 then update it officially to 5.1

He told me to Install this : https://www.androidfilehost.com/?fid=95916177934554226
He also told me that there are many ways should help including to restore the system.img (4Gb+) But, he is not sure about it.

So, I thought to ask you guys ??

Thanks in advance.