How to reset notebook file to not to pick deleted environment varaible

I have developed a server extension to input a value in Jupyter Lab UI and save it to environment variable (using python os library). I will use this variable value in notebook files execution in Jupyter Lab. User can delete this value in UI which deletes it from environment variable (using del in my extension code). After deleting this environment variable also the current working notebook file has access to this value. How can I reset the current working notebook to not to pick deleted environment variable.

JupyterHub - Used helm chart version “3.0.3” to deploy the 4.0.2 version of application on AWS EKS Cluster.