How i can change the default image?

From Settings:

• Go to settings >> Modal Options
• At the bottom of the settings, You will see Adblock Icon Section at the bottom
• Make Sure your enable icon settings
• Select Custom Icon, After that You will see the field to upload the image.

Using Code:

/**
 * Change Adblock Icon
 * 
 * @package chpadsblockpro
 */
add_filter("adb/change/html/icon", function($iconCode, $iconAlernativeFile, $iconAlernativeAlt){

    $imageType = "img";  //svg
    $fileURL = "REPLACE_IMAGE_URL";

    return sprintf('<img class="chp_ads_blocker_detector-icon %s" src="%s" alt="%s">', $imageType, $fileURL, $iconAlernativeAlt);
    
}, 10, 3);