How to delete a VNIC in free-tier instance, if possible.

Summary

I placed an instance in a public subnet, and now want to change it to a private subnet.

Content

Hello,

Please excuse me if this is not the correct forum for this question.

In the free-tier, I have two  VM.Standard.E2.1.Micro instances in a public subnet.

Now I want to move one of them to a private subnet.  Can this be done, or do I have to recreate the compute instance?

I'm guessing I would have to delete the VNIC attached to the instance and create another one in the private subnet, but there is no "Delete" option in the VNIC details page.