There may a way to do this directly in SSRS but I would try to do this in your dataset query if possible.
The following query recreates your dataset and then adds an extra column GroupByID
which you can then use in your report to easily group the data.
The first part of the query is just to produce some data, you only need the main SELECT part and you can swap @t for the name of your table.
DECLARE @t TABLE(Relevo char(1), ID int IDENTITY(1,1), Turno varchar(10), TT float)
INSERT INTO @t(Relevo, Turno, TT) VALUES
('A', 'NOCHE', 0.085),('A', 'NOCHE', 0.1),('A', 'NOCHE', 0.099),('A', 'NOCHE', 0.055),('A', 'NOCHE', 0.07),
('A', 'NOCHE', 0.076),('A', 'NOCHE', 0.102),('A', 'MANANA', 0.06),('A', 'MANANA', 0.065),('A', 'MANANA', 0.064),
('A', 'MANANA', 0.126),('A', 'MANANA', 0.136),('A', 'MANANA', 0.107),('A', 'NOCHE', 0.059),('A', 'NOCHE', 0.121),
('A', 'NOCHE', 0.063),('A', 'NOCHE', 0.055),('A', 'NOCHE', 0.056),('A', 'NOCHE', 0.085)
-- Change @t below for the name of your table
SELECT z.Relevo, z.ID, z.Turno, z.TT, MIN(z.GroupByID) AS GroupByID
FROM(
SELECT
a.*, b.id AS GroupByID
FROM @t a
LEFT JOIN
(SELECT * FROM (
SELECT
*
,LastEntry = IIF(LEAD(Turno,1,'') OVER(ORDER BY ID) = Turno, 0,1)
FROM @t
) x WHERE x.LastEntry = 1
) b
ON a.Relevo = b.Relevo and a.Turno = b.Turno and a.id <=b.ID
) z
GROUP BY z.Relevo, z.ID, z.Turno, z.TT
ORDER BY ID
This gives the following output

Now all you have to do in SSRS is add a parent row group, grouped by GroupByID
and add the expression you required (e.g. =AVG(Fields!TT.Value)
).
The report design will look like this...

NOTE: I am showing the first column for clarity but you can delete this.
The final output looks like this.
