The way to uninstall Magisk -- like to install a new version -- is to flash the Magisk uninstall file in TWRP. Then install new version.
What was your purpose?
If you wanted to go back to full stock for some reason, not be rooted, not have TWRP custom recovery, you would flash the KDZ in Dev Patched LGUP.
You got into Download mode before opening up LGUP? That's the best way. Get into Download mode first, THEN open up Dev Patched LGUP.
Also are you using the Pie compatible Dev Patched LGUP? It's the one with the devset.bat file and you open from desktop shortcut. It's NOT the one where you had to replace the .dll file manually.
If you're not sure, uninstall the LGUP and reinstall the one from any Pie KDZ thread, even the T-Mobile H932 Pie KDZ thread.
If that doesn't do anything, then someone with T-Mobile H932 will have to help you. This variant doesn't have normal fastboot flash commands.
I appreciate the help and just tried this version installed correctly.
My device is recognized during the bootloop, reaches 4% in LGUP and then reboots into download mode. Once in download mode it is unrecognizable by the PC "ERROR open port 0x200, Port open error (COM3)" failing the installation.
The download mode on the phone looks very empty, it says "Now waiting for any connection" and never changes. Below that shows "Unknown B74" which seems in increase in number, and shows "Unknown / E / L / R0".
I'm trying to flash H93230d. My phone is never recognized in LGUP while in download mode, only in bootloop.