If you wish to force a specific currency other than USD in any OptimizeMember Pro form, you’ll simply need to edit the shortcode that is generated (note that you must use the pro form shortcode generator and not a membership order button element).
You’ll need to view the shortcode and find the cc=”USD” attribute and just change it to your 3 letter currency abbreviation.
Note: Please ensure that your payment gateway is setup to accept the currency you would like to have the pro form accept. Some payment gateways such as Authorize.net, Stripe, and Paypal may have some limitations on which currencies are accepted and may have other requirements you need to meet in order to start taking payments in those currencies (an example would be that Paypal generally requires that you maintain a balance in the currency you wish to accept).