You can do that by changing the excel column type…
Or
Read the data then loop and use assign inside loop as currentrow("date") = currentrow("date").Tostring.Replace(".","")
Or currentrow("date") = datetime.parseexact(currentrow("date").ToString,"dd.MM.yyyy",System.globalization.cultureinfo.invariantculture).ToString("ddMMyyyy")
Check in log message if the input format of date is same else chnage accordingly dd.MM.yyyy is ehat you need yo change if you see a different format
1. Read the excel sheet and store in dt1
2. use invoke code with dt1 as In/Out arguments with below code
dt1.AsEnumerable().ToList().ForEach(Sub(row) row("date")= DateTime.ParseExact(row("date").ToString.Trim,"dd.MM.yyyy",System.Globalization.CulturalInfo.InvariantCulture).ToString("ddMMyyyy"))
3. Then u can use write range to write the updated dt1