An edit: Here's pictures that should help because it might be awhile til i can do a video Lol

A good shot of new (pin or blood) feathers coming in. You can see the casings covering the new feather inside. For feathers at this stage, i would only preen the tips open.

Here's a good shot of the casings on feathers a bit more ready for help. The casings are fairly clear so you can see where the blood flow stops. You can safely help them preen away anything ABOVE that line with no issues at all. They actually enjoy the extra cuddling and bonding. And just like clipping a dogs nails, I usually stop a bit away from the blood line just to be safe. As long as you don't remove casing below that line, you won't hurt them.
IF a feather should get preened too low (either by you or sometimes they over preen themselves) and it's bleeding and won't stop, take a pinch of corn starch or flour (basically the same thing as the pet store product Quik Stop) and apply pressure to that feather. If it bled a little but then stopped, it should be fine. Young birds often get over excited when preening themselves (because it's itchy!) and this can happen. Wing feathers are ones that will pulse blood right out of them and that bleeding would need to be stopped.
A good shot of new (pin or blood) feathers coming in. You can see the casings covering the new feather inside. For feathers at this stage, i would only preen the tips open.
Here's a good shot of the casings on feathers a bit more ready for help. The casings are fairly clear so you can see where the blood flow stops. You can safely help them preen away anything ABOVE that line with no issues at all. They actually enjoy the extra cuddling and bonding. And just like clipping a dogs nails, I usually stop a bit away from the blood line just to be safe. As long as you don't remove casing below that line, you won't hurt them.
IF a feather should get preened too low (either by you or sometimes they over preen themselves) and it's bleeding and won't stop, take a pinch of corn starch or flour (basically the same thing as the pet store product Quik Stop) and apply pressure to that feather. If it bled a little but then stopped, it should be fine. Young birds often get over excited when preening themselves (because it's itchy!) and this can happen. Wing feathers are ones that will pulse blood right out of them and that bleeding would need to be stopped.