To switch between eSIMs:
For iOS: Go to Settings > Cellular, tap the eSIM you want to use, and select it as your default line for cellular data. You can also enable/disable specific eSIMs.
For Android: Go to Settings > Network & Internet > SIM cards, select the eSIM you want to use, and set it as your default for data, calls, or SMS.
You can have multiple eSIMs installed but only one active at a time for data.