So, right now you can’t really do that right off the bat.
Existing GitHub issue
There is an existing GitHub issue asking for OpenAPI 3.0 support on OWASP ZAP, but currently (at the time of writing) that is still open: https://github.com/zaproxy/zaproxy/issues/4549
First, you’ll need to get OWASP ZAP
Then, get the OpenAPI support plugin
Here’s a post that explains API exploration via OWASP ZAP: https://zaproxy.blogspot.com/2017/04/exploring-apis-with-zap.html
OpenAPI 3.0 to Swagger 2.0
You can use this API Spec Converter tool for conversion: https://github.com/LucyBot-Inc/api-spec-converter