How could I get the last value of a column header in Excel based on the filled data?

Hi nishant. For example, I have an excel file with
A,B,C as column headers:
1 2 3
4 5 6
7 8 9
with values like that.

Then i put a read range excel function and put ("A3:??), but I dont knot the last column letter header because it might change.(for this example is C but it might change due to the scenary of my process).

The same happens with the last value in C3 which is “9” but it might change if another coworker adds more information. I need to put that "read range " based on that.

Lets say that tomorrow the file changes to this:

A B C D E
1 2 3 p q
4 5 6 r s
7 8 9 t u

Readrange(A3:??) Is that possible i mean robot could get the columb header letter and the last number of that column (E3). Its the number 3 but how?