The instructions for setting up the EmonTx with the ESP wifi module are here:
Reading through that, it looks like the IP address of the EmonTx WiFi module is not important to the configuration of the Emon system, as long as it can communicate with the EmonCMS endpoint (your EmonPi).
To change the WiFi network they are connected to, you need to connect to each one individually and change the WiFi settings (as per the guide above). You should be able to use your current DHCP table from your router to work out which IP addresses your devices are using so you can point your browser at them directly.
EDIT: I noticed the following on the Github page for EmonESP:
If re-connection fails (e.g. network cannot be found) the EmonESP will automatically revert back to WiFi AP mode after a short while to allow a new network to be re-configued if required. Re-connection to existing network will be attempted every 5min.
So you may have to power down your “old” WiFi access point once you have the new one running and then go through the initial WiFi selection setup from the setup guide to reconnect it to your new WiFi network