AIS eSIM2Fly Worldwide Roaming Partners
AIS has published a list of the worldwide roaming partners. While updated infrequently, it will give a rough idea of the network your eSIM2fly will be connected to in each country. Multiple carriers in each country mean any of them will work.
Manual Network Setting
AIS does make it is possible to manually select your network. If you find you are in a location and your network choice is switching between carriers or not connecting, you can do a manual network selection.
Go to Settings > Cellular > Network Selection.