Trying to round off 4 corners in a rectangle

I’m new to modeling— trying to model an indoor football field ( the same dimensions as a hockey rink )

I’ve got a cube set to the x and y dimensions and i’ve flattened down the z axis…

…for the life of me I can’t figure out how to round the edges of the rectangle ( would probably be around 25 to 35% )

Can someone please explain the process for me



If I get you right you should try to bevel the vertices with Ctrl+Shift+B,
here is a short video

hope it helps