Hi @Nicolas Aguilera,
It sounds to me like you need to have a custom form that sends both an event and updates the customer property. Do you have a developer that can help you?
I would suggest looking at this: https://developers.klaviyo.com/en/reference/track-post
So whenever the event happens you could trigger a flow.
I'm not a developer myself but have worked with many to get custom integrations done. The documentation of Klaviyo is very clear. If you know which data you'd like to sent to Klaviyo a dev should be able to help you easily. If you have the opportunity, use a serverside solution.
Regards,
Omar Lovert
Polaris Growth
Helping E-commerce brands maximize Lifetime Value & Profits with Klaviyo, CRO & CVO - Get your free Audit - https://link.polarisgrowth.com/free-audit