Hello,
First you have to create EmailMessage object and set all the values in the created EmailMessage change object like To, From, Content, Subject etc. This EmailMessage object you have to send as input parameter to the SUB_SendEmail microflow.
If incase if your using any EmailTemplate then inorder to replace the tokens, after setting the values in EmailMessage object, then you have to retrieve the respected EmailTemplate and fetch the tokens list & replace the tokens if it does exist.
For more details refer this documentation https://docs.mendix.com/appstore/connectors/email-connector/