This article explains how to change the preset emoji complexion in the Facebook Messenger app.
Steps
Method 1 of 2: iPhone

Step 1. Open the Messenger app, depicting a white lightning bolt on a blue background
If you are not logged in, type in your phone number, tap "Continue" and enter your password

Step 2. Tap Home
It is located at the bottom left.
If Messenger opens a conversation, first tap the "Back" button in the top left

Step 3. Tap your profile photo
It is located in the upper left. This will open your profile.

Step 4. Tap Photos, Videos and Emojis
It is located at the bottom of the screen.

Step 5. Swipe right on the Messenger Emoji button
This will activate the Messenger emojis, which are slightly different from the iOS ones.
If the button is already green, skip this step

Step 6. Tap Emoji Settings at the bottom of the page

Step 7. Touch a skin type
This way the selected color will be applied to all emojis that allow you to customize the complexion.
You can also touch and hold an emoji on the emoji keyboard to see the different options associated with the complexion
Method 2 of 2: Android

Step 1. Open the Messenger app, depicting a white lightning bolt on a blue background
If you are not logged in, type in your phone number, tap "Continue" and enter your password

Step 2. Tap the Home button
It is located in the lower left corner.
If a conversation opens, first tap the "Back" button in the top left

Step 3. Tap the profile icon at the top right

Step 4. Tap Photos & Media
It is located under the profile photo, next to the camera icon.

Step 5. Tap Emoji at the bottom of the page

Step 6. Touch a skin type
The selected color will be applied to all emojis that allow you to change the skin tone.