I have this meter 31906EA9, and I've downloaded the latest firmware file

i.75.98.1.bin

Where can I find the instructions on how to install this firmware?

The current installed firmware is ATV1.73.6@MX1290

Please refer to https://www.iammeter.com/docs/firmware-upgrade

Please note :

When you flash the new firmware to the old product which firmware version is before 1.75.70, it exists a probability that bricking the energy meter.
The fault would occur in such case
1: the energy meter is powered down before the upgrade is complete.
2: the web browser is closed before the upgrading is complete.
3: new upgrade start before the upgrade is complete

These probabilities indeed exist, although it is very low.

If the customer encounters the situation that the device cannot operate normally due to the failure of the firmware upgrade, we will not bear any responsibility.