How to get Image/Asset URL in Matrix?
I'd suggest giving the Matrix templating docs a once-over.
If steps is the name of your Matrix field, then {% for row in entry.steps %} is going to be looping over each of the Matrix blocks you've defined.
Then you'd want to check for the stepImage asset field in the correct block. i.e.
{% for block in entry.steps %}
    {% if block.type == 'myBlock' %}
         {% set image = block.stepImage.one() %}
       
         {% if image %}
             {{image.url}}
         {% endif %}
    {% endif %}
{% endfor %}