I would suggest that you click on the following link to get an overview of the task ahead of you
https://hbr.org/2013/05/six-components-of-culture
In any case, you would require the top management buy in for a comprehensive Corporate Culture initiative to be put in place.
I would suggest that based on your understanding of what you gather from studying the article in the link, prepare a broad outline of the relevant areas pertaining to your corporation.i.e.
1 Vision & Mission
2.Values
3.Practices
4.People
5.Narrative
6.Place
Keep in mind that you would have to reorient your existing employees to embrace this corporate culture and also ensure that the corporate culture must be a key factor to be kept in mind when fresh recruitment are made.
Trust the above input will enable you to draft a comprehensive plan of action.
Best Wishes