There's no need to describe the whole medical story. You need to give the carrier practical information: who travels, on which connections, where you meet and what assistance is needed.
Hello, on the link [number] of the day [date] request assistance for the blind passenger. I need an escort from [meeting point] to [train, bus or gate] and confirmation of the place and time of the meeting.
When you travel with your partner
They're both supposed to have the other person's phone number and an arranged place to reconvene. In a busy area, you can split up: the passengers are waiting in a safe, clearly named place, while the partner deals with information, ticket or change in staff. You don't leave without a word or a vague "I'll be right back."