Locked cell edit

In the C1W4_Assignment of course DeepLearning.AI-TensorFlow-Developer-Professional-Certificate, I edited the locked cell by pressing the tab so now i am unable to submit the assignment please help.
PS- i also teried to delete the cell and inserting a new cell but the locked cell is not getting deleted also.

Certain notebook cells are marked as uneditable since the staff don’t want you to change the cell contents. This helps the grader work without any hickups and prevents learners from making incorrect assumptions about the assignment.

Feel free to change cell metadata for personal experiments (see this link)

Please follow these steps to refresh your workspace