want to access field "Text1" under "Row1" section. I can do it with $item.Fields["Text1"].Value But there are another section which also contain Text1 field. How can access specific field under specific section.
This is impossible; you should use field IDs if you want to do this.
It would be best to name the two fields unique values.
Field names must be unique. If fields are defined on a single data template with the same name, then a validation error occurs when the data template is saved. But fields can also be inherited from base templates, so an item can potentially contain multiple fields with the same name. If this occurs, Sitecore displays both fields in the Content Editor, but programmers, who use the field name to retrieve contents when using the API and XSLT Renderings, might get unexpected results.