No module named 'Tkinter'

[snippsat]

Even when I did all the steps CMD is giving me the answer: "C:\Users\Αλέκος Βαγιώνης\venv\Scripts>pip install tkinter
No Python at D:\Applications\Python 3.7.2\python.exe"

You shall not install tkinter,on Windows Python versions it's always build in.
Now you are running from venv virtual environment,do you know how this works?

I think you should look at Python3.8 (3.6-3.7) and pip installation under Windows.
The basic command that most work in cmd if use Python 3.7:

# Test python
C:\>python -V
Python 3.7.2

# Test pip
C:\>pip -V
pip 20.0.2 from c:\python37\lib\site-packages\pip (python 3.7)

# Test tkinter
C:\>python
Python 3.7.2 (tags/v3.7.2:9a3ffc0492, Dec 23 2018, 22:20:52) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import tkinter
>>>
>>> print(tkinter.__doc__[:200])
Wrapper functions for Tcl/Tk.

Tkinter provides classes which allow the display, positioning and
control of widgets. Toplevel widgets are Tk and Toplevel. Other
widgets are Frame, Label, Entry, Text,
>>> exit()

C:\>