// get the role by id:
const mutedRole = message.guild.roles.cache.get('');

// or, if you can't get the id:
const mutedRole = message.guild.roles.cache.find(
 (role) => role.name === 'Muted'
);

// if there is no `Muted` role, send an error
if (!mutedRole)
 return message.channel.send('There is no Muted role on this server');