the error means that the dotnet executable is not in your path. just type
% echo $path
it see if its on the list. you don't specify how you installed the sdk (homebrew or the sdk installer), but the sdk uses /usr/local/share/dotnet. the sdk typically creates an entry in /etc/paths.d to define the addition to $path, but you can use your shell config. again you don't specify your shell, but it looks like the bash shell rather the current default, zsh.
if set up correctly, from the command line you should be able to run
% dotnet --info