I have an old and damage sidewalk with a heater wire inside it.
The wire is cut somewhere but I don't know how to find where. Is there any electrical tool or way to find where is it cut?
This is an example of a wire in a sidewalk:
Yes there are scanners that can read through concrete and even metal conduit, but they are expensive the one I use is a greenlee CS-8000, I just did a quick search and new these are ~750$. You may be able to find a used one for much less, these are awesome for finding a broken wire even in rigid metal conduit, through walls, identifying circuit breakers even if the power is off. There may be other brands/models out there but mine has saved me hundreds of hours and I have found faults that 2 electricians before me could not find , the difference was I have this simple but high accuracy tool.
A non-contact voltage detector may be able to help you if you remember or have pictures of the cable from before the pour.
I have no idea how you think you're going to repair it if you find it though, cutting the concrete open will also cut the cable again.