What would be a way to get someone with bipolar help?

Would encourage. That person to accept psychiatric assessment. It is important not to tempt that person with alcohol or illicit drugs.
How severe? It really depends on the severity of the illness. If there is a risk of harm to self or others or if there are any psychotic symptoms then hospitalization is the best answer. If the symptoms are mild and there are no other risk factors, outpatient treatment might be sufficient. That means they need to be seen by a psychiatrist.