Might not be possible currently, @Nico Kearns. 

Online iD eSIM help & support articles don’t seem to cover this process, merely how to change from an eSIM to physical SIM card. 

Hi @Nico Kearns 

You’ll be able to switch from an existing physical SIM card to an eSIM at any time, you’ll need to request a replacement eSIM which can then be activated.

Tom

Can I request a replacement esim

This forum article explains how to do this, @Roger Perfield. 

Hi @Roger Perfield,

Welcome to the Community!

I hope that the article has assisted you with your query.

If you require further assistance, please let us know.

Kash