Add an average line to an existing indicator

I have an indicator that shows the price movements of the last 12 periods.
It is divided into three periods, day, week and month.

Your task is to add the lines of the 12 periods and divide by the number of periods (12). So we have shown the typical price trend of the last 12 periods.
Furthermore, this line should then be displayed in the current period.

An example: the following graphic shows the price development of the last 12 months. It starts in last Month November and each color represents a month.




Now comes the part you are responsible for. You now use the lines of the 12 periods (months) and make a line that shows the average of the last 12 periods (months) . I have recreated this in the following image with a yellow line.