• You implemented updatename as a method, but you're not calling it as a method. I'm not sure why this is a method at all.
• You used curly braces around your arguments where you should have used parens.
• You have curly braces around $keyvalue when you shouldn't.

my %HoH = ...;

sub updatename {
   my ($keyname, $keysubname, $keyvalue) = @_;
   $HoH{$keyname}{$keysubname} = $keyvalue; 
}

updatename("flintstones", "husband", "joe");
# or
# updatename(flintstones => husband => "joe");
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