Can't be changed where? You should probably provide a bit more context.
Well own server that runs in vps ubuntu contabo traccar server v 6.8.1 i have a gps tracker tkstar 905 that runs in hubao protocol and the time that appears in my server web ui is about 8 plus utc time .I senn the command about timezone and nothing happens the time keep on utc +8.The other trackers i used in my server coban tk star903 tkstars 915 protocol watch or 103 time are the same and wright to all them.
You can configure timezone on the server side. See the decoder.timezone
configuration option.
I have an issue with my own server the tk star 905 tracker is online but the timezone cant be changed