Although the baby has become congested and can have a bit of trouble breathing the baby can still breathe through their mouth so there's no way for the baby to actually suffocate from being congested.
Many babies become congested and although they have a bit of difficulty breathing they still can breathe enough to keep them alive and keep them from suffocating.
For the baby to die of not being able to breathe their airways would have to be completely or at least nearly completely closed off.
That doesn't happen during congestion so the baby is safe.
When a baby is congested you should use a humidifier in the babies room at night and during the day when they are in the room to add moisture to their lungs and nasal passages.
Also using a nose vacuum to suction out some of the mucus to help keep the babies nose clear can help.
Within a week or so the babies congestion should go away and the baby should be able to breathe properly again.
You can also give the baby some baby safe nasal spray or nasal drops to help clear the congestion.