Edit Person Account Layout in Lightning Experience

To do so following the steps:

1. Switch to Lightning Experience
2. Go to Account object.
3. Select any Person Account Record
4.Click on the Gear Icon | Select Edit Page | Users will be redirected to the Lightning App Builder
5. Customize the components based on the requirement
6. Click Save
7. Click Activation
8. Click App, Record Type and Profile.
9. Click Add Assignments
10. Select the Lightning Apps that should reflect this layout
11. Click Next
12. Select the Record Type of the record that should reflect the changes
13. Click Next
14. Select the Profiles of the users who should see the layout
15. Click Next and Save.
 

Once you go back to the record by clicking ( ← ) you will see the changes applied. There is no need to repeat the add assignment when making changes afterwards just make sure to Click  Save.

Notes:

The Lightning App Builder page has two aspects:  

1. Home Page: To edit home page, follow the steps :

Click Home Page | Click on the Gear Icon | Select Edit Page | Users will be redirected to the Lightning App Builder  To edit

2. Record Page: 

Go to Any Record Page |Click on the Gear Icon | Select Edit Page | Users will be redirected to the Lightning App Builder (Record Page)


See Also: 

Page Layouts in Lightning Experience
Create and Configure Lightning Experience Record Pages