To set your expectations, the platform does not have this option and requires custom development. 

If the requirement is on top priority for your website, you will have to connect with your personal developer to make the required changes.

As a workaround, you may use the following CSS code. Please see the steps below. You can check the 

Font Cheatsheet here.

1. From WordPress admin page, go to Appearance > Customize

2. Click the Additional CSS tab

3. Append the following:

.messages-wrap i.bb-icon-inbox-small:before {
  content: '\e979';
}

4. Save changes 

Note: Any modifications are considered as custom work already. Know more about our Support policy here: https://www.buddyboss.com/support-policy/