put/set somebody's mind at ease/rest
put (one's) mind at ease
To reduce or remove one's worry, anxiety, dread, fear, etc. I know you're anxious to hear how your father is doing after the surgery, so let me put your mind at ease—he's going to make a full recovery. That bonus really put my mind at ease about these debts.
set someone's mind at ease (about someone or something)
to make someone feel mentally comfortable about someone or something. Alice is upset. I will have to do something to set her mind at ease about the accident. Please set your mind at ease. Everything will be all right.