Photoshop layer mask - how to bring back to the subject what you took away with the background brush

I am pretty new to using Photoshop, and have been learning through the in-app tutorials, and now that I've completed those, through Youtube tutorials. I am currently following along with a tutorial on how to remove background from an image, and I spent about an hour and a half yesterday removing the extra bits and pieces between the leaves of the flower image that weren't taken out with the quick "Remove Background" tool. Now that I've done this I notice there are some pieces of the flower and leaves that are black, and I don't know if I did this when I was using the brush, but I can't seem to figure out how to bring back those parts. I don't want to undo all my work but I don't like the look of random chunks being painted into the black background when I'd like to just get them back into the image. I have looked this up everywhere and every tutorial on how to get back the background you erased seems to be on a different version of Photoshop, they said to press "option" or "alt" while using the brush tool to get back the lost parts but that didn't work. I thought there was an inverse brush that allows you to paint back what's under the layer mask from the background you painted in. Sorry if I'm not explaining this right, but I'm still figuring out what all these tools do and I could really just use some help in finding what tool to use to bring back just parts of the image that I painted into the background. So if you're a Photoshop expert and you know what I'm fumbling to explain, it would be so awesome if you could help me figure this out. (You may be able to see the chunk of the leaf that was painted into the black background in the image I am trying to remove background from.) Any help would be so appreciated.