ux integration: how to collaborate and define a new style guide for an existing corporate design?

As a naive ux designer, I am having trouble defining a style guide. There is an existing style guide made with Adobe XD. As a team effort, we would like to improve and manage the style guide. A reasonable and productive solution is to use Frontify. Unfortunately, the company runs out of budget and we need to look for an alternative that can provide the same features as Frontify.

Does anyone face the same problem?