eSIM conversion usually means one of two things, and the difference matters for travellers.
The first is converting a physical carrier SIM into an eSIM: keeping your existing number and plan but swapping the plastic card for a digital profile on the same phone. Most major carriers support this from their app or a store visit, and it is a one-way housekeeping step, handy when you buy an eSIM-only handset. It has nothing to do with buying data abroad.
The second is what people really ask about a travel eSIM: can you switch it back to a physical SIM, or move it between SIM types. Here the answer is no. A travel eSIM is issued as a digital profile only; there is no physical version to convert to, and most travel profiles are single-install, so deleting one to convert it can use it up. If you need to change phones, that is eSIM transfer, not conversion, and support should reissue the profile.
In practice you rarely need to convert anything. Your home SIM and a travel eSIM run side by side through dual SIM: the physical SIM keeps your number for calls, the eSIM carries data abroad. Check your handset on the device compatibility page, then follow how to install an eSIM.