Click on another vertex or pad you want to align the unaligned vertex with. The coordinates of the other vertex or pad will be memorized and will serve as a basis for aligning the vertex. Then click on the vertex you want to align. Press F7 or F8 depending on the alignment axis (X or Y) you want to use.
Select unaligned vertex. Click F3 to align the connected trace segments at 180°, 135°, 90°, 45° or 0° angles between segments.