How to say Dear (FIRSTNAME) in e-mails?

Hi,

I would like to use variables in Woocommerce order process and completed mails.

I want to see Dear Firstname, thanks for your order.

I tried several things like:

{customer_first_name} [first_name} $first_name

Is there someone who knows the right code?

Thanks a lot!

https://www.ads-software.com/plugins/woocommerce/