How to ignore the NA values in a dataframe when the auto.arima

I have the code to run the auto.arima in a small dataframe, however, in some columns I have several 'NA' values (ranging from 1990 to 2003, for example). How do I establish in my code that such values are ignored? >

bra.ts <- ts(CSV_BRA, frequency = 1, start = c(1990), end = c(2016))

taxa <- ts(BRA$TX_CS, frequency = 1, start = c(1990), end = c(2016))
# Comando para indicar a regressão

covariates <- c('RURAL', 'AMZ', 'N', "VALUE_N", 'AREA')

fit<- auto.arima(bra.ts[,"TX_CS"], xreg = bra.ts[,covariates], stepwise = FALSE, 
                 approximation = FALSE)
fit

  

DATAFRAME

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