1. If you use tabs somewhere other than at the beginning of a paragraph, write back. Otherwise...
2. Use the Replace feature to delete the tabs. Ctrl+H
   Find text: ^t
   Replace text: (nothing)
   Replace All
3. Take a look at the Style of your text.
   Understanding Styles in Microsoft Word
4. Modify the Paragraph Style to include the First-line Indent paragraph formatting that you want.
5. If your style is the normal style, you may want to, instead create a new style with the paragraph indent based on normal and use that style for your text.