How is it possible to automatically fix the timezone of all users, per the country that they are in?

Summary:

Right now, all users have UTC as their time zone. However, we have users located in different countries, thus, they are in different time zones. How is it possible to automatically fix the timezone of all users as per the country that they are in, without the need for each and every user to manually fix it? We have 3000+ users in the company, so it is not feasible to do it manually.

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Version (include the version you are using, if applicable):

23C

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