I agree with the other replies. Although symptoms of an MS episode, or relapse, can develop quite quickly, they are not usually life-threatening, and I find it difficult to imagine a situation where emergency first aid would be necessary, or, indeed, useful.
People with MS may be more at risk from falls, depending on the degree to which they are affected, but if the person were to have a fall, you would treat it the same way as anybody else having a fall - there are no special precautions for dealing with someone with MS, that you wouldn’t do for anyone who is injured. In some cases, sensation, including that of pain, may be diminished in some parts of the body, so the person might underestimate the seriousness of an injury, or even not notice at all - because it didn’t hurt. So how much pain the person is reporting might not be a reliable indicator of how badly they are hurt. But a good first-aider should know that anyway; they would not rely solely on the patient’s own reports, but would take additional steps to assess the seriousness of the injury.