sheet cannot be found - excel

Question

I have a working macro which changes a linked sheet in a cell according to month. Say from April to March.
From
='C:\Data\Name\[Time.xlsx]2021-04!A1"
to
='C:\Data\Name\[Time.xlsx]2021-05!A1".
This works as long as the user remembers to add a new sheet at the beginning of each month, which is not always done in time. As a result i get a "sheet cannot be found -> choose one from below" Prompt". How can I avoid this selector and add a "table not found" string in the cell instead and move on to the next operation in the loop?
Thanks!
EDIT:
Code Added upon request:
Sub Month()
Set rngB = Range("B2:B6")
strColB = "Range("B1")
iRowB = 1
strMonth = InputBox ("Insert Month as integer","Month")
strMonth = Trim(strMonth)
For Each cellB In rngB
cellB.Formula = "='C:Data\[" & strColB & "Time.xlsx]2021-" & strMonth & "'!B" & iRowB
iRowB = iRowB + 1
Next cellB
End Sub

Answer 1

Here's an easy function to test if a sheet exists prior to accessing its cells
Function SheetExists(ByVal SheetName As String, ByRef InWorkbook As Workbook) As Boolean
On Error Resume Next
SheetExists = Not InWorkbook.Sheets(SheetName) Is Nothing
On Error GoTo 0
End Function
Here's how you would use it.
Sub test()
MsgBox SheetExists("2021-04", Application.Workbooks("Time.xlsx"))
End Sub
Another example:
Sub test()
If SheetExists("2021-04", Application.Workbooks("Time.xlsx")) Then
'do stuff
Else
[a1] = "table not found"
End If
End Sub
Edit:
After the code was added to the original post. Here is an example of how to implement this function with that code:
Sub Month()
Set rngB = Range("B2:B6")
strColB = Range("B1").Text
iRowB = 1
strMonth = InputBox("Insert Month as integer", "Month")
strMonth = Trim(strMonth)
For Each cellB In rngB
If SheetExists("2021-" & strMonth, Application.Workbooks("Time.xlsx")) Then
cellB.Formula = "='C:Data\[" & strColB & "Time.xlsx]2021-" & strMonth & "'!B" & iRowB
Else
cellB.Formula = "table not found"
End If
iRowB = iRowB + 1
Next cellB
End Sub