Auto fill specific cells from userform

Hi

I am trying to create a spreadsheet to record vehicle mileage at the end of each week, however sometimes we cannot input the information until 2 or 3 weeks later. I am looking for a way to auto fill specific cells when the user inputs the information using a userform.

On the attached spreadsheet:

The first button input an 'Empty Row' ready for the new week and current mileage

The second button opens the userform to select the vehicle, date and input the mileage

I cannot figure out how to have the mileage inserted into the correct cell irrespective of when we insert the information.

Any help to modify the code would be very much appreciated

'find  first empty row in database
iRow = ws.Cells(Rows.Count, 1) _
  .End(xlUp).Offset(1, 0).Row

'copy the data to the database
ws.Cells(iRow, 1).Value = Me.txtVRN.Value
ws.Cells(iRow, 2).Value = Me.txtmileage.Value