How to align the edge in straight line. I tried align with S Y 0, The shape of my mesh got disturbed. Any way to align the edge without disturbing the mesh.
The underlying geometry is quite interesting and needs to be cleaned manually.
You need to join vertices with J key to create clean lines. New edges are highlighted with red in the image below.
Next you need to dissolve remaining out of place edges shown in the image below. This can be done by selecting the edges, pressing x and selecting Dissolve Edges.
The remaining line is quite clean.