Holt winters Alpha - holtwinters

Question

I am trying to get the HoltWinters Alpha function added.
I have a Table called Sales1 and the code should refer to this table.
Is there anyone who can correct or amend my code below ,so i get the Holtwinters Alpha instead of the Chronbachs Alpha?
Holt winters calc (need this probably amended)
library(forecast)
library(Metrics
)
read_file(sales1)
x <- sales
x = c(Sales1)
mSES = HoltWinters(x, alpha = 0.5, beta = FALSE, gamma = FALSE)
mHW = HoltWinters(x, alpha = 0.5, beta = FALSE, gamma = FALSE)
mSES$SSE
mHW$SSE
HoltWinters(x, alpha = NULL, beta = NULL, gamma = NULL,
seasonal = c("additive", "multiplicative"),
start.periods = 2, l.start = NULL, b.start = NULL,
s.start = NULL,
optim.start = c(alpha = 0.3, beta = 0.1, gamma = 0.1),
optim.control = list())
chronbachs alpha calc
read_file(sales1)
library(tidyverse)
library(psy)
Number of rows before to take into account
rolling = 2
sales1 <- sales::sales( ~date, ~sales,)
#Lag
sales1 = sales1 %>% mutate(lagsales = lag(sales))
#Rolling Chronbachs Alpha.:( I need the Holtwinter Alpha here )
sales1$alpha = c( rep(NA, rolling),
map_dbl((rolling + 1):nrow(sales1), function(x){
cronbach(sales1 %>% select(sales, lagsales) %>% slice((x-rolling):x))$alpha
})
)
sales1
tibbet from Sales1 table:
df <- tibble::tribble(
~seq, ~date, ~sales,
1, "3/01/2017", 40,
2, "4/01/2017", 2,
3, "5/01/2017", 2,
4, "6/01/2017", 2,
5, "7/01/2017", 30,
6, "8/01/2017", 2,
7, "1/02/2017", 9,
8, "2/02/2017", 5,
9, "3/02/2017", 65,
10, "4/02/2017", 3,
11, "5/02/2017", 65