Replacing SD Card

Required Tools:

Phillips Head or T8 bit screwdriver
Strong fingernails, tweezers, or needle-nose pliers to remove the old SD card
The ability to read/write a 64gb microSD card (unless pre-flashed card is acquired)

In the event that your microSD card fails, here are the steps to re-flash it or replace it with a brand new one:

Unplug and remove the 4 screws from the bottom of the unit using a Phillips head screwdriver (Note that 1st gen Hotspots will need a T8 bit screwdriver, and also have a gps antenna wire attaching the top plastic to the board, this should stay connected.)
Carefully remove the installed microSD card located by the fan - tweezers or needle-nose pliers may help with this. (see image below)
Format the new card or re-format the existing card into ExFat format.
Download and install a program to Flash the card such as Etcher, if needed: https://www.balena.io/etcher
Download the image file to Flash: https://helium-nextgate.s3-us-west-2.amazonaws.com/artifacts/2021.06.14.0-sdcard.img.gz
Unzip the file.
Use Etcher to Flash the newly formatted microSD card with the file.
Place the newly flashed card back into the card reader slot.
Plug the Hotspot back and and confirm that it boots up.
Screw the Hotspot back together.

Unplug and remove the 4 screws from the bottom of the unit using a Phillips head screwdriver (Note that 1st gen Hotspots will need a T8 bit screwdriver, and also have a gps antenna wire attaching the top plastic to the board, this should stay connected.)
Carefully remove the installed microSD card located by the fan - tweezers or needle-nose pliers may help with this. (see image below)
Place the pre-flashed card into the card reader slot.
Plug the Hotspot back and and confirm that it boots up.
Screw the Hotspot back together.

If successful, everything should boot up normally.

A card like this would work, but anything comparable would also suffice.
You can also buy pre-flashed ones from Parley Labs.