I have one nostril blocked and the other one I can breathe out of, how can I decongest the blocked one?

Caution. If this is a cold and short lived circumstance, a shot of nasal decongestant spray in the blocked nostril can give your relief. You do not want to do this more than 2-3 times a day for no more than 3-4 days. Nasal saline spray is safe and shold be used first. Use it liberally. Oral decongestants can help but we are trying not to use these due to side effects and potential abuse issues.
Nasal sprays. If it's acute try saline spray and an oral decongestant. Use of a topical or oral decongestant should be limited to less than a week or you can develop what is called rebound which only blocks it more especially with topical sprays. If it is chronic see an otolaryngologist or facial plastic surgeon to evaluate by exam. Www. Asc. Psd. Com.