Install python kali linux

 $ sudo apt-get install python

if python3 is installed and shows python not found 

then just use the bellow command 

$ sudo apt install python-is-python3

See caveats: python-is-python3 package in Ubuntu 20.04 - what is it and what does it actually do?

A simple safe way would be to use an alias. Place this into ~/.bashrc or ~/.bash_aliases file:

alias python=python3