Click on the 'IMAGERY' icon on the left-hand side tool bar.

Click on the 'NOTES' button on the top right-hand side of the screen.

Click on the three dots next to the Notes name and select the "Edit layer" option. You can see what objects are already in your note by tapping or clicking a Note’s name to expand it.
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The note editing tools will appear on the bottom middle of the screen, where you can select between the pin, line, and shape options.

If you would like to edit an existing object, click on the three dots next to the name and press 'Edit", and don't forget to save changes.