How do I reconnect my Iphone 11 SIM, after using an eSim while travelling?

If you see No Service or Searching on your iPhone or iPad

1. Check your coverage area. Make sure that you're in an area with cellular network coverage. ... 
2. Restart your iPhone or iPad. Restart your device. ... 
3. Check for a Carrier Settings update. ... 
4. Take out the SIM card. ... 
5. Reset your Network Settings. ... 
6. Update your iPhone or iPad. ... 
7. Contact your carrier. ... 
8. Get more help.

If you see No Service or Searching on your iPhone or iPad ...

Remove your SIM card from the SIM card tray and then put the SIM card back. ... Make sure that the SIM tray closes completely and isn't loose. If you use a SIM tray from a different model iPhone, iPad, or from another phone manufacturer, it might not fit properly.

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad ...

Learn what to do if you see a SIM not supported alert.

To be able to use any SIM across the globe you must have "No SIM Restriction" against Network Provider Lock. Please refer to the pic below.

Hmmm.

That’s unfortunate … traveling should not normally affect other SIMs/eSIMs.

And you indeed should be able to turn it on/off at will.

You might try Reset Network Connections.

Beyond that, assist from your carrier will likely be needed.

Go to Settings/General/VPN & Device Management and see if there is a leftover profile for the foreign eSIM. If there is, tap on it and delete it.

I suggest that you contact your local cellular carrier and check with them all the parameters in:

Settings>Cellular>Cellular Data Network (specifically APN).

Regards

Giulio