Unable to assign interface object pointer in golang

I am making a function that will unpack arbitrary variable types from a variadic parameter into variables like so:

package main

import (
    "fmt"
)

func unpackVariadic(variadic []interface{}, into ...*interface{}) {
    for i, v := range into {
        *v = variadic[i]
    }
}

func Update(variadic ...interface{}) {
    var a, b interface{}
    unpackVariadic(variadic, &a, &b)

    a = "Hey"
    b = "Hello"
}

func main() {
    a, b := "Hola", "Hola"
    Update(&a, &b)
    fmt.Println(a)
    fmt.Println(b)
}

However, it is printing "Hola", "Hola" instead of "Hey", "Hello" how I would like.

My understanding is that a and b in Update() and main() have different reference values, meaning reassigning from within Update() will just locally assign a and b from the addresses of original a and b to the values of the new strings.

To solve this, I tried reassigning a and b by their object pointers:

func Update(variadic ...interface{}) {
    var a, b *interface{}
    unpackVariadic(variadic, a, b)

    *a = "Hey"
    *b = "Hello"
}

But, when I do, I get invalid operation: cannot indirect a (variable of type interface{}).

So, why am I unable to assign by object pointers in Update() while I am allowed to in unpackVariadic? How could I go about this differently?