Create a time stamp

Hi Fanis_Georg  - Instead of overwriting the old data, you can configure Power BI to append the new data to the existing dataset

extract the data, Home > Get Data > Text/CSV. load your initial dataset (e.g., the first week's data). Now in power query editor, duplicate the initial query by right-clicking it and selecting Duplicate.Name one query "CurrentWeekData" (for new weekly uploads) and another "AllData" (for the cumulative dataset).Select Append Queries as New.Append the "CurrentWeekData" query to the "AllData" query.

add a custom column in table, add a new column with timestamp as like below:

Timestamp = DateTime.LocalNow()

add another column 

WeekNumber = WEEKNUM([Timestamp])

one mre for year

Year = YEAR([Timestamp])

last one more new column , 

WeekYear = FORMAT([Timestamp], "yyyy-[Week]")

these helps in If you already have historical data saved elsewhere, you can manually import it once and append it to the cumulative "AllData" query.