Given a flextable without a header how can I add a header?

If I have a flextable without a header, how can I add one? In the example below I am setting the scenario up artificially. i.e. I would like to turn flexiris_without_head back into flexiris_with_head.

library(flextable) # version 0.9.2

flexiris_with_head <- flextable(iris)
flexiris_with_head

flexiris_without_head <- flexiris_with_head %>%
  delete_part(part = "header")
flexiris_without_head

If anyone is interested in more context:
I am primarily working with huxtable objects, which I, however, need to translate to flextable objects for docx output purposes. Using huxtable::as_flextable() leaves me without a (technical) header, which is an issue for long tables because the headers do not roll over to the next docx page anymore.

Here is one way how we could do it using add_header_row():

library(dplyr)
library(flextable)

# flextable
df <- flextable(head(iris))

# iris without header -> df
df_without_header <- df %>%
  delete_part(part = "header")

# adding header to flextable
df_with_header <- df_without_header %>%
  add_header_row(
    values = colnames(iris), 
    top = TRUE
  ) %>%
  hline_top(part = "header") %>%
  hline_bottom(part = "header")

df_with_header