Seasons are long
If you start the season on the bench, the first thing to do is to keep your hopes up. A championship is long and your coach will surely need everyone's help. Keep this in mind and rest assured that you will have an opportunity to show your worth. Try not to let your frustration get the best of you so that you have a better chance of being called up. Blaming your coach and complaining that they made a mistake won't get you anywhere. In most cases, they make decisions for the good of the team and feel no ill will towards you.
So it's your job to figure out why you're not starting. It's important to be self-aware in the most neutral, objective way. If necessary, try having a discussion with your coach so that they can help identify any shortcomings that you have to overcome. Once you know which areas you need to improve, there's only one thing to do: get to work.
You have to focus on yourself, without obsessing over your competition. Have fun during training and try to improve your performance without analysing every move the starting player in your position makes. This is the basis of healthy competition in which you can work peacefully and feel excited to train.