One way is to select the vert loop and then scale to 0 along that axis that you are aligning to - like in forward view global, a row of verts from top z to bottom z could be scaled to 0 in x axis to straighten them.
After you do this, sometimes the effect isn’t what you had in mind because of the resulting mesh deformation - I see that you are working with subsurf on, and if the subsurf is what you are arriving at , then the placement of the edges will change that resulting form.
You could try edge slide also. Ctrl-E for the menu.
Also, making a new edge loop can be accessed through K for the cut menu, as well as directly with Ctrl-R ( hover over the mesh in the area you want to make the new loop to preview, then click once and move the mouse to slide the new loop. Also, scrolling the mousewheel will add multiple loop cuts to save time)