Please review Getting good answers to your questions.
You need to help those in this community willing to help you by providing some information. You don’t give us much information to go on to advise you. What system are you using? What did you use to install Jupyter and Python? Had it worked before? What else you’ve read and tried of issues similar to yours? (For example, the title of post here is very similar. What makes your issue different?) You posted this under ‘JupyterLab’ topic. Which version of JupyterLab?