[AC Question]

I want to give this phone to mom and before I do that I want to reset to original factory settings with no LTE anymore

It was rebooting by itself anyway and she does not need LTE

How do I do that?

[Rukbat]

Whether or not it gets LTE is based on the modem firmware it's running (basically the version of Android) and the hardware in it. LTE isn't an app you can disable or uninstall. (And LTE won't make it reboot by itself.)

As far as her "not needing" LTE" - if she uses mobile data, and your carrier uses LTE, she needs LTE. (LTE is like 4G+ - something that almost all carriers use now. Eventually they may do away with 3G equipment, and 3G-only phones will be useless for data.)

Get the reboot problem fixed and the phone will be ready to use. (She can't get a no-data plan on a Smartphone, so there's no reason to disable LTE capability.)