VBScript doesn't have a goto statement. Since your filename is being built based on time I would just loop while the file exists and then move on. In theory that shouldn't take more than a second.
Code:
Sub CreateOutputFileName
    Dim strFileName
    
    Do	
        strError = ""   
        strFileName = "NBS" & Month(now) & Day(now) & Year(now) & "-" & Hour(now) & Minute(now) & Second(now) & ".csv"
        strFileName = strOFolder & strFileName
    Loop While fso.FileExists(strFileName)

    Set tsi2 = fso.CreateTextFile(strFileName, 1)  
End Sub