There is currently no reliable way to root this phone without a computer. Here is a thread from XDA forums (I am a Sr member) that tells you what to do. I will warn you this phone may brick and become unbootable
This is the ONLY guide I would trust. Matter of fact XDA (&Rootjunky.) are the ONLY places I trust for rooting and higher level tech advice.
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I worked on this project a lot. It works. Be sure to follow the steps EXACTLY. I've had more people emailing me about bricking their devices than I can count.
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One thing, when replacing the superuser, Kinguser (malware crap) be very careful because I don't know anyone who has been successful flashing factory firmware on this.
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There are no custom ROMs I'm aware of for this. you can take a Nandroid backup, but you can't use it since this version of TWRP cannot see the SD card.
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This phone is an old piece of garbage that is used in the Obama Phone programs. very slow and little storage. I smashed mine.
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Better to find a plan that letz you bring your own phone to a carrier that will let you. I'm only aware of Safelink (350 min, unlimited text 1gb data free on progam, I spend $45/month for unlimited everything with them.
There is currently no reliable way to root this phone without a computer. Here is a thread from XDA forums (I am a Sr member) that tells you what to do. I will warn you this phone may brick and become unbootable
https://forum.xda-developers.com/android/general/howto-zte-quest-n817-locked-bootloader-t3587174
My advice, toss this piece of junk and find a better $20 phone