You can change the notification icon by setting NotificationRequest.Android.IconSmallName

using Plugin.LocalNotification;
using Plugin.LocalNotification.Core.Models;

var notification = new NotificationRequest
{
    NotificationId = 100,
    Title = "Test",
    Description = "Test Description",
    Android =
    {
        IconSmallName =
        {
              ResourceName = "my_icon",
        }            
    }
};
await LocalNotificationCenter.Current.Show(notification);

after that add "my_icon.png" to Resources/Images

after that add "my_icon.png" to Android Project Resources/drawable

Set the small icon to use in the notification layouts. Different classes of devices may return in different sizes. See the UX guidelines for more information on how to design these icons.

Please follow Google's Design Guidelines https://material.io/design/platform-guidance/android-notifications.html#behavior