I think this is tricky when your kiddo also can't admit they are anxious. We find that keeping everything calm before competitions helps - getting their early - but not TOO early, having gum, and reminding her of positive things she's been working on to boost confidence seems to help. I think a post competition slogan that has helped a lot has been to JUST say, "I really enjoyed watching you play today". No comments on abilities (even if they were amazing), just joy in watching participation. I've noticed this has made small stacking strides for our oldest. Finding ways for her to connect with her teammates also helps her feel more confident.