Need to know how to add a black line at the bottom to Excel for printing

I have an excel file that whenever I print, I have to manually go to each page's bottom to add in the black border line at the bottom because the data I input tends to shift the pages. I need someone to teach me how to create a border (or any other ways??) around my excel checklist that will automate a black border line at the bottom when I print. Sometimes I have over 100 pages where I have to manually insert the black bottom lines. Please note I am an old person with minimal computer and Excel skill so the explanation has to be simple and clear - even a short youtube video recording to show may help.