I’d recommend these steps:

1) Go to setup -> object manager and go to Account Object

2) click on Actions on the left and creat a new action

3) Name the action “Account Plan” and set it as an action to update record

4) set your layout fields with all the fields you want to see in that section for Account Plan

5) Save the action

6) From within Account Object still, select lightning pages on the left and edit the lightning page

7) click on the tabbed area and add a new custome section (Name it “Account Plan”)

8) add a “related record” section from the left side into the open area within the new tab

9) set the action to you new action of “Account Plan” and voila