This article from Software Tricks provides a step-by-step guide on how to modify emoticons (icons) in Facebook Messenger.
Step 1: Update Messenger to the latest version through AppStore and Play Store.
Step 2: After that, open any conversation on Messenger.
During your conversation, press and hold any message for 3 seconds to reveal the emoticon icon, then select the Add (+) option.

Step 3: When the emoticon window appears, choose Custom (1) and proceed to select each icon in the list (2) to make changes.

Step 4: To make the most of all the emoticons, select the emoticon sets below the tool bar (1) and choose Done (2) when finished.

Step 5: Congratulations! You've successfully customized the emoticons in Messenger. Now, press and hold a message for 3 seconds to experience the newly set emoticon pack.

Note: Facebook Messenger now features Double Tap, similar to Instagram. When you double-tap a message, the emoticon icon will appear. The emoticon shown after a Double Tap will be the first icon in the settings list.

In this article, Software Tips shares how to customize emoticons in Facebook Messenger. Wishing you all a delightful day!
