Follow this step by step to add an existing Plan or create one in a Teams channel
Add a Planner tab to a team channel.
|Note: You can't add a Planner tab to a private channel in Teams.
In your team channel, select Add a tab +.
In the Add a tab dialog box, choose Tasks by Planner.
In the application dialog box, choose:
Create a new plan to make a new Planner plan and add it as a tab to this channel.
Use an existing plan to choose an existing Planner plan to add to a tab in this channel.
Choose whether to post to the channel about the tab, and then select Save.