M Power Query: how can I reuse a function between multiple queries?

Ok so I figured it out :)

I go to the left pane where the queries are

right click

new query -> blank query

copy pasted my function code from above

REMOVED the name of the function from the code, letting only the parenthesis + parameter remain at the top

 (dateTimeValue) =>
                let 
                    convertedValue =        
                          if dateTimeValue >= DateTime.FromText("2016-03-27T02:00:00") and dateTimeValue < DateTime.FromText("2016-10-27T03:00:00")
	then
		//summertime (+2 hours from UTC)
		dateTimeValue + #duration(0,2,0,0)
	else if
                dateTimeValue >= DateTime.FromText("2017-03-26T02:00:00") and dateTimeValue < DateTime.FromText("2017-10-29T03:00:00")
	then
		//summertime (+2 hours from UTC)
		dateTimeValue + #duration(0,2,0,0)
	else if
            dateTimeValue >= DateTime.FromText("2018-03-25T02:00:00") and dateTimeValue < DateTime.FromText("2018-10-28T03:00:00")
	then
		//summertime (+2 hours from UTC)
		dateTimeValue + #duration(0,2,0,0)
	else if
                dateTimeValue >= DateTime.FromText("2019-03-31T02:00:00") and dateTimeValue < DateTime.FromText("2019-10-27T03:00:00")
 then 
	//this is summertime, 
	//add +2 hours to get Stockholm summer time
	dateTimeValue + #duration(0,2,0,0)
else
	//this is wintertime
	//add +1 hours to get Stockholm winter time
	dateTimeValue + #duration(0,1,0,0)
                in 
                    convertedValue

Then i changed the name of the query itself to be the name of the function

convertUTCDateTimeToStockholmTZ

All other queries in this Power Bi project can now reuse that function. Great!

Here is an explanation