Many. It depends on what you mean by poor breathing. If what you mean is asthma or a lung disease such as copd, careful treatment with your doctor is imperative. Others with heart conditions can have shortness of breath. If sleep apnea is the issue, the most commonly prescribed treatment is cpap. Oral appliances that keep the lower jaw slightly forward may also help.
Three major ones. CPAP which is a machine that keeps your upper airway open by forcing room air in through your nose and/ or mouth, surgery to correct upper airway abnormalities, or an oral advancement device that moves your jaw forward to allow more room for air to enter in through your oropharynx. Best wishes.