tony@timac ~ % cd gptj                                                                                                                                                                                                                 
tony@timac gptj % . ~/venv-gptj/bin/activate                                                                                                                                                                                              
(venv-gptj) tony@timac gptj % jupyter-lab

Run the following when you are finished with the virtual environment

(venv-gptj) tony@timac gptj % deactivate