$ pip3 install virtualenv
If this raises an error, try installing sudo apt install python3-venv
Create a new virtualenv
$ python3 -m venv <envname>
Activate the environment
$ . <envname>/bin/activate
Install all the dependencies from requirements.txt
$ pip3 install -r requirements.txt
You can exit the environment by typing
$ deactivate
I you modify the project using new libraries you might install, update the requirements.txt file
$ pip3 freeze > requirements.txt
For further questions, please consider reading the related documentation here.