For starters, as many others stated, you should store all timestamps either timezone aware (ie. store the timezone, not just the date), or “naive”, but in that case, convert it to a well-known timezone first (the best one is UTC).
How to display it to the user is a different story. There are numerous ways to do it, like converting every date on the backend side, or employ the frontend for this. One frontend example may be the awesome Moment.JS library.