In a microflow you can retrieve all the records you want, based on the same criteria as those that are shown in your screen or any other (sub)set. Loop over these objects to update the ‘CER no’ attribute to your desired value. Refresh (and commit if desired) the list and you’re set!
Also, if these are the type of problems you run into, I recommend going through the Mendix Academy online learnings: in the long run they’ll save you a lot of time :)
Good luck!