How to suppress warnings "Command underbar has changed." and "It is better to use one of the extsizes classes, if you can."?

I would like to use an Overleaf template (https://www.overleaf.com/latex/templates/tagged/rsc), but it gives a warning for the underline command of sectsty. Do you have any idea how to suppress all the warnings of this package? I am using the pdfLaTeX compiler. What I tried is the following:

usepackage{silence}

WarningFilter{latex}{Command}

but it doesn’t work. I have the same problem with the following message:

ExtSizes Warning: It is better to use one of the extsizes classes, if you can.