This is frankly the actually difficult part of the process. ISO20022 is just a way to send messages, your actual commercial and settlement arrangements still need to be done. Banks are not required to provide such a service, you will specifically need an arrangement with a bank that offers that. Or more likely with an intermediary like Wise which will abstract the distractions like ISO20022 away from you.
In the EU the PSD2 directive explains which market parties can apply for access to these systems. Which usually means you need to have a company that has interest in this kind of access and provide service to third parties. Unfortunately i think PSD2 only sets technical rules for authentication. Not for the actual API. So the bank might not give you direct access to SWIFT but to an API that abstracts it instead.
AFAIK, Wise has currently stopped allowing payments through its API[1] for private persons due to regulation, and there don't seem to be any other worldwide providers to do so.
[1] You can send prepared payment orders to Wise, but still need to log in and manually approve them.
