To do this in Chrome Dev tools you can use the Geolocation sensor emulation.
Go to the 3 dotted menu, More Tools and Sensors.
There’s a Geolocation dropdown with some common locations but you can change your preferred one as well. To do that you can choose Other… in that dropdown and enter a custom Timezone ID
Here’s a demo page to test it: https://mathiasbynens.be/demo/timezone
and a video that shows the procedure: https://www.youtube.com/watch?v=pIpN_AuV4AI
