https://www.vetinfo.com/nasal-congestion-in-dogs.html
Nasal congestion in dogs may be a consequence of a respiratory infection; however, the congestion may also be caused by other factors such as allergies. It’s important to detect the problem and prevent it from becoming chronic or causing complications.

Causes of Nasal Congestion in Dogs:
–   A nasal congestion in canines is often caused by a respiratory or a sinus infection. The infection may be caused by bacterial, fungal or viral agents. Other possible causes of a stuffed nose may include:
–   Allergic reactions to pollens from the outdoors or chemicals from your home
–   An object stuck in the nose
–   A dental infection that has spread to the sinuses

Symptoms of Nasal Congestion :
If your dog has a nasal congestion, you will notice that he will have a hard time breathing and may hold his mouth open in order to get air. However, there may be additional symptoms involved, which can point to the possible underlying condition causing the congestion. Watch out for symptoms such as:
–   Sneezing and coughing, which can indicate a respiratory infection or allergies
–   Halitosis or bad breath, which occurs if the dog has a dental problem
–   Swollen and red gums
–   Pus pockets under the gum line
–   Nose bleeds
–   Watery eyes or various types of ocular discharges (monitor the color and consistency of the discharges, which can help in the diagnosis)
–   Itchy skin
–   Pawing of the nose and mouth
–   Excessive drooling
–   Lethargy

Diagnosing Nasal Congestion:
A vet will perform an examination of the dog and detect the possible medical problems leading to a nasal congestion. The results of blood tests can indicate the presence of an infection. The composition of the ocular or nasal secretions will reveal the nature of the infection. An intradermal testing is run if the vet suspects allergies. If the dog has an object stuck in his nasal passages, an x-ray is needed to establish the exact location of the object.

Treatment Options for Dog Nasal Congestion:
An allergic reaction can be managed with antihistamines, steroids and topical creams that will reduce the skin symptoms. If the dog is affected by a sinus or a respiratory infection, a 7 to 14 day cure of antibiotics will be prescribed. Ensure that your vet is aware of the possible antibiotics your dog is allergic to when prescribing the treatment. Don’t discontinue the antibiotic treatment if you see your dog’s condition is improving. This can result in immunity buildup to the taken antibiotics and the infection may strengthen and the infectious agents may not respond to similar antibiotics. Antifungal medication is recommended if the vet establishes that the infection is fungal. Your vet will also advise you to use some nasal sprays or saline drops and steam baths. These will relive the congestion, at least temporarily.

Response from Dr Kathy when an ME dog owner asked what to use: 
Please discuss these options with your veterinarian:
1) “Little Noses” pediatric saline nose drops may help.
2) Elevating her head and front of her body during sleep may help – elevated platform and Pro collar – look in “feeding/sleeping..” album in the photos section
3) A pro-motility drug may help her stomach empty more quickly, minimizing residual acid in the stomach and possible reflux and regurg
4) Sucralfate LIQUID for possible esophagitis
5) After AP under control, nebulizing 1-3 times daily may keep her bronchioles open to encourage the coughing up of “stuff” that she may aspirate.