I think that you can try revert Python to default version. Than everything should remain ok
Or this.. I also suggest to wipe everything and start over..
Before your next journey with Python, make a backup 
I made a backup of my whole PC before installing Zorin but I don't want to start over.
How should I reset python?
Did you install it using Apt?
Then you could try back pedalling each step you took.
Do not forget to remove ppa you have added manually as well.
Yes, I installed it with apt. But I don't know how to remove it now. I use the xterm terminal emulator for fixing but I don't want to use it primarily. I want to get the gnome console back and roll back my changes to python.
Ah, that's right.
You do not have any working terminal at the moment.
Can you try installing Sakura in Software?
It is a great alternative terminal.
Why? I am using XTerm at the moment.
I am confused.
You do have a terminal which can open?
I have a terminal emulator: XTerm. But I want to use the gnome terminal.
I uninstalled python3.9 AND python3.6. Now I reinstalled python3.6 but it doesn't start because files are damaged or something like that. I found the problem but I am not able to make changes to the files.
OK, thanks for the clarification.
Since I cannot read your mind 
it is better to give as much information as you can when you ask for help.
Did you remove
deadsnakes ppa
as well?
How should I remove it?
sudo add-apt-repository --remove ppa:PPA_Name/ppa
Change PPA_Name to whatever the ppa you have installed.
I need full access to the system files to add a shortcut.
Sorry, you lost me again.
I thought we are talking about removing ppa.
I typed the command and an error occurred. It didn't find the directory. It seems to be removed.
Did you type exactly like this?
sudo add-apt-repository --remove ppa:deadsnakes/ppa
I need the shortcut called python3 which is connected with the python3.6 file. When I type python 3 in the console it says that the interpreter at /usr/bin/python3 has a defect. The python3 file redirects to another shortcut in /etc/alternatives/python3 which redirects to python3.9 which doesn't exist. Now the shortcut disappeared completely. I have to get the rights to edit these directories to fix this. After that it should work.
Yeah.