how to apply intervention analysis to my time series?

I have weekly sales data for a restaurant, with 113 observations, and every year in January, sales drop significantly and then recover after two or four weeks. I applied a SARIMA model with auto-arima in R, but when I evaluate my model, I realize that the residuals are not constant and not normally distributed. Box-Cox Transformation was already used, lamba was 1.99 but it did not improve the model.

Upon reviewing a time series text, I learned that I need …

analysis apply arima auto-arima box-cox data datascience distributed normally sales sarima series text time series transformation