I feel that the best way to control you anger especially while in a relationship would be to apolgize, even if it wasn't your fault and just get some space, take a walk or just sit in another room. Sometimes people just need some alone time to rethink why they're actually mad.
If you just have to punch something, do it to your mattress or pillow, anything that won't leave an ugly mark or break your hand. If you can hold it in, just inhale and exhale SLOWLY because it will relax you. And just remind yourself things like "Ok, is this really worth getting angry about?" (assuming it's nothing dead serious).