I found a car toyota echo 2000 model ,183000kms done so how i came to know about timing belt changed or not

The 2000 Toyota Echo has a timing chain, not a timing belt. You don't need to change it.

Good day,first of all you may ask the owner if he has the service manual so you can change the last timing belt changed. secondly you may try to check the belt itself if it has some tiny cracks or a little loose or a little worn. hope this helps, have a nice day