If you have enabled Zoom in your Doodle account settings, all meetings booked from Doodle will contain a Zoom link which can be found in the calendar invitation and the calendar event.
By default, your Zoom account should have the "meeting passcode" setting on already. If it doesn't, or if you are not sure, double check your Zoom settings here www.zoom.us/profile/setting and make sure you have the setting below enabled:
Once a Doodle meeting gets scheduled and a Zoom link is created, the password of the Zoom meeting will be in the Zoom link itself (
?pwd=xxx) and there is no need for the Doodle organizer to send out a password manually. Just by clicking on the Zoom link with the encoded password, the participants will have access to the Zoom meeting.