Hi,
you can try the below snippet.
add_filter('uwp_social_login_button_html', 'uwp_social_login_button_html_custom_call', 10, 3);
function uwp_social_login_button_html_custom_call( $btn_output,$provider_id,$url ){
if( $provider_id == 'facebook'){
$btn_output = '';
$btn_output .= "<br/>";
$btn_output .= '<li class="uwp_social_login_icon">';
$btn_output .= "<a href=\"$url\">";
$btn_output .= '<img src="https://i.ibb.co/VHhbmD5/download.png" alt="Sign in with facebook" class="w-auto">';
$btn_output .= "</a>";
$btn_output .= "</li>";
}
return $btn_output;
}
make sure to replace the image URL with the proper image.
Regards