Kellermann’s wonderful strike against Yeovil Town on Saturday was enough to secure Cook his first win since returning to the club.
“We were good in parts but we can still improve in other bits but we are adjusting still,” the midfielder said.
"It has been a difficult period but we are coming through it now.
"The gaffer said before the game that we have had our lull and that this was the first brick to build back up to where we want to be and we have done that tonight.”
The Spireites have changed formation to 4-2-3-1 recently and Kellermann believes they are starting to get to grips with Cook’s ideas.
Kellermann explained: "He (Cook) has been great, he has brought his own freshness to everything.
"He has come into a tough run of fixtures straight away but I think you can see little changes happening on the pitch. I feel like we are a bit more fluid.
"He has put his own stamp on it and everyone is just adjusting to it now.”
In the last few matches Kellermann has been playing a much deeper role alongside Tom Whelan and he says he is enjoying their partnership.
He said: "It is better being alongside him than playing against him!
"He is a great player, technically he is unbelievable,
“As long as he keeps having good games, he is going to get us results and my job is to make sure he has a good game.
"I have had a couple of months where I have been playing a bit higher, I have played right wing-back a few times recently, I have been trying to form again, I don’t think I have been great in the last month or so.
"Today I was back to myself and I feel more comfortable doing the role I am doing at the moment.”
On his superb winner against Yeovil, he added: "One of my mates has sent it to me, it is nice, it looks good!
"My job is more defensive but I am happy I have been able to help the team drag us through a game and get us three points.”