How to "find and replace" text?

A solution will be to:
sed -i "" 's/oldword/newword/g' mynotebook.ipynb

Found here: Is there a way to default to "Replace in all cells" in the "Find and Replace" in jupyter?

UPDATE:

with the latest version of Jupyter lab (>1.1.4) this function is added!

Just click "Find", below the "Edit" menu: a contextual window will appear at the top right of the notebook.

There you click on the small arrow at the left side of the text field, and the "replace" function appear.

OLD ANSWER (still good anyway):

At the end, I found this solution, but it's only for those who know how to use VIM, the text editor.

I installed an extension, jupyterlab-vim, and so I can use VIM commands for search and replace text.

This appears to be an overkill as solution, but for VIM lovers (like me) using many VIM commands in Jupyter Lab is just fabulous.