You can't personally remove the copyright strike but anything that is copyrighted such as music is off limits unless you get permission from the copyright holders. That's why it's best to use music that is free to use or create all the elements in your video.
After a few months they get removed if it was a copyright strike, but you can't remove it yourself. Also you can't use anything you like without the proper permissions. You wouldn't like to make something awesome and get it stolen from you and someone else made money out of it right?