How to use footermarginsize{} in Overleaf?

I am writing a letter and want to keep signature on the same page. In this question it is suggested to add footermarginsize{10pt} line. However it works badly – Overleaf says that it is undefined control sequence and it leaves the line "10pt" above the address but actually it does the trick and signature remains on the same page. How can I achieve correct work of that function?

Using usepackage[scale=0.75, footskip = 10pt, includefoot]{geometry} does not help to keep signature on the page.