Hi @wu cong? , thank you for your question!
Hover and drag the "NA;" to get the suggestions. Select Replace as shown in the screenshot
Here, it selects all the occurrences of "NA;" Add the step.
In case this selection is not occurring, then please Edit the step and make sure that the "Match all occurrences" check is selected as shown in the screenshot
I hope this helps. Please do reach out to us in case you are having any issues.
Best,
Apeksha