Short answer
The eSIM connects automatically after it is installed correctly, turned on, selected for mobile data, and connected to a supported local network in the destination.
Check this first
The eSIM line is turned ON.
The eSIM is selected for Mobile Data / Cellular Data.
Data Roaming is ON for the eSIM line.
You are in the supported destination for your plan.
Before arrival
The eSIM may show Activating or No Service before it reaches a supported local network. This can be normal.
Important
Do not delete the eSIM while trying to activate it.
If it still does not work after arrival, contact support with screenshots of the eSIM settings and your current country/city.