You want to send an email to a particular list of people, who are in Plezi but drowned in the mass of your contacts.
To create a list in Plezi, you need to
either select criteria ("smart" list) ;
or import & create a static list by giving a name to your list at the time of mapping (see screen).
In this case, the best practice is to create an "email DD/MM" field, in the form of a checkbox (which you can delete afterwards) and to fill it in during your import.
Note: for the "checkbox" field to be checked, you must indicate "Yes" in the column corresponding to the field.
Thus, you can then create a smart list from "Marketing > Contact list" with the criterion "email DD/MM" checked.