reassure (one) of (something)
To make one feel confident or assured about something; to make a promise or guarantee about something to one. They went to great lengths to reassure me of the security of my job after the completion of the merger. He reassured me of his devotion to our marriage.
reassure someone of something
to promise or guarantee someone something. Kelly reassured her friend of her support in the election. Please reassure Tom of our continued support.