Yes, you're right. Here is the code.
if(!require("astsa")) install.packages("astsa")
require(astsa)
library(readxl)
library(ggplot2)
rotac<-x[c(1:35),c(1:2)]
rot <-ts(rotac[[2]], start = c(2018,1), end = c(2020,11), frequency = 12)
rot
plot.ts(rot, ylab = "Ret", xlab = "Mes", col="blue")
boxplot(rot)
class(rot)
fit<-decompose(rot, type = "mult")
autoplot(fit)