See this program as an example:

package main

import "fmt"

const (
  a = iota
  b
  c

  iota = 0

  d
  e
  f
)

func main() {
  fmt.Printf("%v, %v, %v, %v, %v, %v \n", a, b, c, d, e, f)
}

This program outputs 0,0,0,0,0,0 since all references to iota resolve to the iota constant defined inline.

If you mean to reset or offset builtin.iota, either start a new constant definition or use an expression involving iota as the constant value. For example:

package main

import "fmt"

const (
  a = iota
  b
  c
)

const (
  d = iota + 42
  e
  f
)

func main() {
  fmt.Printf("%v, %v, %v, %v, %v, %v \n", a, b, c, d, e, f)
}

This program outputs 0,1,2,42,43,44 as builtin.iota is reset at the beginning of a new constant declaration and then the offset of 42 is applied to the last three constant specifications.