Val cannot be reassigned error in constructor

Question

I want to reassign a new value in the constructor, but I can't.

class InstantDate {

    private var date: LocalDateTime? = null

        constructor(date: String) {
        if (date.contains(" ")) 
        {
            date = date.replace(" ", "T")
            this.date = LocalDateTime.parse(date)
        }
    
    }

}

I get the error "val cannot be reassigned."

How can I solve this without creating a new value? Thank you.