To write the basmala or to write the basmala in a dream indicates that the dreamer is a person who loves Allah's creations and accepts them as service to him.
If a person sees that he writes basmala in his dream, it is said that that person will gain wisdom, attain guidance, and take his place among the beloved servants of Allah. It means that the dreamer will become a great person in the future, people will take inspiration from him and bow down in front of him with respect.