Planners and your account
From the Overview tab on your dashboard, create an invite link and send it to your planner. It works for seven days. They open it, and they are in your dashboard, editing the same plan you see.
Your planner works inside your dashboard, not in a separate tool. You invite them with a link.

Until it is used, the invite shows in the same card with the days remaining, and you can cancel it. An unused link is real access, so it should be revocable.
If your planner cannot accept it yet, nothing is lost. The link stays open for its seven days and works the moment they can take another couple.
Either of you can end it. You remove them from the same card; they can remove themselves.
If your planner connects Google Drive, a planning sheet of your wedding appears on the Overview tab, kept in their Drive and shared with you. See What is the planning sheet?.