This is currently for ISO weeks only, but if you have the week number, the weekday and year and you want that date in return, you can use this function below. And according to ISO, Monday is 1 and Sunday is 7.
CREATE FUNCTION dbo.fnGetDateFromYearWeekWeekday
WHEN @Year < 1900 OR @Year > 9999 THEN NULL
WHEN @Week < 1 OR @Week > 53 THEN NULL
WHEN @Weekday < 1 OR @Weekday > 7 THEN NULL
WHEN @Year = 9999 AND @Week = 52 And @Weekday > 5 THEN NULL
WHEN DATEPART(YEAR, DATEADD(DAY, 7 * @Week + DATEDIFF(DAY, 4, DATEADD(YEAR, @Year - 1900, 7)) / 7 * 7, -4)) <> @Year THEN NULL
ELSE DATEADD(DAY, 7 * @Week + DATEDIFF(DAY, 4, DATEADD(YEAR, @Year - 1900, 7)) / 7 * 7, @Weekday - 8)