Charlton had been fighting to save their League One status when Holden took over back in December last year.
They were placed 18th in the table back then, but have since managed to climb up to the eleventh spot and have won three of their last five league games.
Assessing the progress of his team, the 27-year-old defender insisted that Holden has been able to bring back confidence.
However, the need is to continue with the real steeliness that they feel they have in themselves, Inniss insists.
“The gaffer has come in and instilled confidence in what we already had in the group and made some changes”, Inniss told his club’s official website.
“Belief is the main thing and that real fight – I feel like we’re more resolute.
“Every player to a man is standing tall, whether it’s the lads coming on or the lads starting games.
“There is that real steeliness about us and we want to continue.”
Charlton are set to take Derby County away from home on Saturday and the visitors will take heart from the fact that they managed to beat the Rams the last time they met them.
