대상 범위의 값을 배열로 변환하고,
배열에 대해서 For x = 1 to Ubound(Data, 1) Step 3  처럼 3줄 단위로 작업을 하고,
for 문 안에서 3개 행을 하나의 행으로 변형하는 작업을 하세요.

추가, vba매크로
----------------------------
아래 코드 중 변경할 부분
시트명: Sheet1
데이터 범위: A1:M15
결과 출력할 첫 셀: A18
-----------------------------
Sub Macro1()
Dim Asht As Worksheet
Dim rngAl As Range, rngIP As Range
Dim xStep%, cntCns%, xGroups%, xGi%, Cn%, xSi As Integer
Dim cntRws&, xR As Long
Dim vDB, Ary() As Variant
Set Asht = Sheets("Sheet1")
Set rngAl = Asht.Range("A1:M15")
Set rngIP = Asht.Range("A18")
xStep = 3
cntRws = rngAl.Rows.Count
cntCns = rngAl.Columns.Count
xGroups = cntRws \ xStep
If xGroups = 0 Then Exit Sub
vDB = rngAl.Value2
ReDim Ary(1 To xGroups, 1 To xStep * cntCns)
Application.ScreenUpdating = False
For xGi = 0 To xGroups - 1
xR = 1
For Cn = 1 To cntCns
For xSi = 1 To xStep
Ary(xGi + 1, xR) = vDB(xGi * xStep + xSi, Cn)
xR = xR + 1
Next xSi
Next Cn
Next xGi
With rngIP.Resize(xGroups, xStep * cntCns)
.ClearContents
.Value = Ary
End With
Application.ScreenUpdating = True
End Sub
 
 
 
혹시 365버전이면 ..
=LET(rngAl,A1:M15, xStep,3, xCns,COLUMNS(rngAl), xSeqs,SEQUENCE(QUOTIENT(ROWS(rngAl),xStep),,1,xStep),
WRAPROWS(DROP(REDUCE("",xSeqs,LAMBDA(xAcc,iseq, VSTACK(xAcc,TOCOL(INDEX(rngAl,iseq+SEQUENCE(xStep)-1,SEQUENCE(,xCns)),0,TRUE)))),1),xStep*xCns))

m365,   offset으로 3줄씩 뛰면서 3줄 가져와서.. torow처리후 vstack

=LET(Area,$A$1:$M$15, step,3, seq,SEQUENCE(ROWS(Area)/step,,0,step),
DROP(REDUCE("",seq,LAMBDA(a,b,VSTACK(a, TOROW( OFFSET(Area, b,0,step,),,TRUE )))),1))

 

파워쿼리로 만들어 봅니다.