Method 'Range' of object _Global error (Error 1004)

Sub multi_guess_and_test()

Dim ws_input As Worksheet
Dim num_rows


Set ws_input = ThisWorkbook.Worksheets("Input")
num_rows = 5

Dim i
Dim j
Dim k
Dim l
Dim set_cell_range As Range, to_value_range As Range, changing_cell_range As Range
Dim to_value_val
Dim temp_val
Dim temp_range As Range

For j = 2 To num_rows
    For i = 2 To num_rows 'i starts at 2 because we assume 1st row is label
    
        k = i + 7
        Set set_cell_range = Range(ws_input.Cells(k, j).Formula)
        
        On Error Resume Next
        l = i + 13
        Set to_value_range = Range(ws_input.Cells(l, j).Formula)
        If Err.Number <> 0 Then
            to_value_val = ws_input.Cells(l, j).Value 'find the value of cell. Even if the cell is a formula, it is ok! (Originally, goal Seek does not allow this cell to be a formula.)
        End If
        On Error GoTo 0
        
        Set changing_cell_range = Range(ws_input.Cells(i, j).Formula)
        
        'now that all the inputs are set, perform goal seek operation
        set_cell_range.GoalSeek _
        Goal:=to_value_val, _
        ChangingCell:=changing_cell_range
        
    Next 'onto the next calculation!
Next
End Sub

i am trying to call values using a for loop and is giving an error please help me.

thank in advance.

Hi and welcome to the forum

Change

Set set_cell_range = Range(ws_input.Cells(k, j).Formula)

to

Set set_cell_range = ws_input.Cells(k, j)

you have dimmed set_cell_range as a range therefore Excel expects to see a range address not something else like a formula.

similar lines of code will also need adjusting.

And purely as feedback I find your variable names quite confusing. The very least I expect of variable names is that they are intuitive. I took me a little while to understand stuff like
Dim set_cell_range As Range.

Think about adopting a naming convention where the initial character indicates the type of variable. I tend to use stuff like

Dim rNames as Range, stManager as String, lRow as Long