Make sure the phone is unlocked before you leave.  You should be able to delete the esim.  I know you can on an Android phone and I'm sure it's the same as Apple.

On the iPhone 14, you can have two eSIM profiles so you would be able to use both for a time. T-Mobile has roaming coverage in Korea, so you can keep both plans going. If you do need to cancel your T-Mobile service, make sure you reach out to have the plan fully cancelled so you don’t run into issues later. Cancelling the T-Mobile plan should remove the number from that eSIM. If it does not free up that eSIM, you can also delete it in settings. 

1. Tap Settings > Cellular.
2. Tap the plan you want to delete.
3. Tap Remove Cellular Plan.

Hope this helps!!

I bought the iPhone14 and the Apple worker said they would easily add my Korean phone number at the store when I arrive in Korea. We had checked that my Korean phone provider was on the list for esim. However when I arrived they said they couldn’t add it if I didn’t remove my T-Mobile plan. They scanned a QR code and it had an error. My phone provider in Korea is KT. What should I do? If I remove the T-mobile plan can I just add it back when I return to the US? Is is complicated? 

i want to do esim on my iphone 11

https://www.t-mobile.com/support/devices/sim-esim

Hi,

I would like to ask about T-Mobile esim I have installed. 
I am using iPhone SE with Soft bank service and physical soft bank sim and I have installed T mobile esim in US. I am in Japan now and want to buy a new iPhone SE. I went to SoftBank yesterday, and they said that I need to check with T-Mobile to ask if the T mobile esim will work on a new iPhone. Will it?

thanks,

What do you suggest for an eSIM plan, which plan, and will this work on an iPhone 13 mini?

All plans should work with an esim.