1) Log into your AT&T account on their website.
2) Go to your main account page.
3) Scroll down to the "My devices" section.
4) Click on "Manage Device" under the phone that currently is using the eSIM.
5) On the My Device page, scroll down to "Options and Settings" section
6) Click on "Manage Your SIM"
7) A menu will slide down, Click on "Switch Devices"
8) On the next page, enter the IMEI number of the phone you want to transfer your eSIM to and click Continue.
System usually takes about 1-3 minutes to transfer in my experience. I've transferred eSIM between my Samsung Z Fold 4 and my 14 Pro Max about 4 times now in the last few months.