How do you approach the task of revamping a brand's voice and tone when the company undergoes a rebranding or shift in strategy?

As with any rebrand, this involves brand strategy -- and the first step to that often involves in-depth interviews with key stakeholders, team members, and customers, gathering as much information as possible. This can also include workshopping and running some fun brand exercises, competitor reviews, etc. 

After that, it's looking at the data and info, and mapping it out in a greater context. This means looking at the small details, but also the big picture: Who and what is this brand in this slice of the market? How is it positioning itself? What are key elements of its personality? 

From there, you can start to drill down to the actual brand identity elements, like voice and tone, by finding adjectives and themes that fit into the overarching brand strategy. Sometimes, it helps to imagine this brand as a person, and describe how they would speak overall, and what tone they would use in different scenarios.