How to convert this line of code.

call the ToString() method of the DateTime variable:

tb_DateFrom.Text = dateIndv.dateFrom.ToString();

Try like this

DateTime dt = DateTime.ParseExact(dateString, "ddMMyyyy", 
                                  CultureInfo.InvariantCulture);
               dt.ToString("yyyyMMdd");

Refer:http://stackoverflow.com/questions/3477735/convert-datetime-to-string-formatyyyymmdd[^]
This may help.

How can you assign a data type to another unless you dont convert it or unless they are not related(or rather cast it to that type). Why can i convert an int to byte? or vice versa?.

Why do i not have ToByte() for every type or can i? or can i not? Why do i have ToString()?

By using ToString() i am converting the DateTime to string format.
If you notice one thing you will find you can call the ToString() on any type. But have you wondered why?

Read the basics of object class. In future you will never ask this doubt my friend. Please dont mind. Just google the stuff brother.

My aim here is not to insult you. I just want that you start learning.

Thanks brother,
Happy Learning.

Just add ToString() for conversion

tb_DateFrom.Text = dateIndv.dateFrom.ToString();

change your code from:-

tb_DateFrom.Text = dateIndv.dateFrom;

to

tb_DateFrom.Text = dateIndv.dateFrom.ToString();