What you will need to do is remove or cover anything where he can see his reflection. When a male cockatiel gets obsessed with mirrors, not only does it cause the behavior issues you are experiencing, but it keeps him in a hormonal state. This causes him a lot of stress because he has the urge to mate. In some cases, a male can actually develop a cloacal prolapse from straining and trying to mate with things. Removing mirrors is the first step. Next, you need to address how you handle him. Always limit petting to his head and neck. When you pet him on the body, it triggers his hormones because normally only a mate would be allowed to do this. You can also try reducing his light to 8-10 hours a day by covering his cage early in the evening. By removing the mirrors and limiting where you pet him, he should calm back down soon and get back to normal. Hormonal behavior is normal, but by being careful not to trigger his hormones, you can limit the behavior.
Thank you for asking Lafeber,