How to downsize an unusual banded ring?

Hi Everyone,

I am using an old ring as a base upon to which to build my own
creations. In this first test case I need to downsize the ring from
a US 8 to a 7 before doing any further work. Typically, a jeweler
would remove a portion of the ring and then connect the ends. In this
case the ring is not a true “ring” - it is a band whose ends don’t
meet but instead pass by each other without touching. That suggests
that I can downsize without any metal removal - Is this possible is
my question? I assume applying pressure with pliers could modify it
at any two points, but I would like to keep the round shape as much
as possible. Any good ideas? (signed) Uncertain and Happy to learn
from the Wise

use a ring mandrel and rawhide mallet. my mandrel is steel, not
plastic. I would put the “ring” at size 7, then hit it with the
mallet to size down. this would keep the correct round shape, etc.