I am no expert but I will try to help you.  It would have helped me more if
you were a bit more specific.  Like would you want the result in the same
cell or a different cell?  if you want it in a differen cell you can use this
formula, insert the date of the first Teusday let's say in cell A1, in cell
B1 write this formula =A1+7.  The following Teusday is always 7 days after
the first Teusday.  Hope this answers you question.