If you wish to include the schema for a YAML file in an existing model, with your model already opened, choose Tools > Reverse-Engineer > JSON document.  

The process includes detection of ISO 8601 date/time/timestamp/duration in strings when target supports such data types.

The structure of a YAML file can be imported either as an entity in the Entity Relationship Diagram, or alternatively as a model definition so it could be re-used in the model:

If you wish to force the destination of the reverse-engineering operation, you may specify the container in which the entities should be inserted.

More information on YAML and JSON Schema here and here.

For RDBMS targets, an additional option appears, that allows automatic normalization of complex data types: