Steve Newport wrote:

What is the best way to take a cutting from a wild elderbeery tree to
plant into the garden?

Don't?!? You will live to regret it in a normal sized garden. Bird lime
with added elderberry is an astonishingly powerful dye.

Buy one of the less vigorous cultivars like dissecta or variagate from a
garden centre. Or find someone who already has a wild one and ask them
to pay you to take away a few hundred of the seedlings that come up
every year. It grows fast enough you don't need to take cuttings.

Regards,
Martin Brown