In the first instance, please make sure you are in “Advanced” mode in WEBUI, on the top right of the page.
After you are in Advanced mode, you can find this setting by going to WEBUI Services → Modbus TCP client → Add instance, scroll down and you will find alarm configuration. There you can change Values, Condition, Action Email or SMS. That way you can set up to receive an email when a certain value changes (please see screenshot attached)