To compose a note, follow the below steps to add a note on a conversation.
Step 1: Once you have selected a conversation you want to create a note on, click on the Note button as shown in the below picture.
Step 2: Click on the input field to start composing a note.
Step 3: After you typed your note you have the option to either save the current note by clicking on the Save button or to delete the note by clicking on the Bin button as shown in the picture below.
Step 4: Once you have chosen to save the note. It will appear on the contact card as shown in the picture below.
* Also note: Once you have saved a note, you will not be able to delete the note at all.