Hi friend,

re:
> Hello Michael, what is the procedure you used to fix it?

The process goes like this - select the polyline, then run Edit > Separate to break its segments into individually selectable separate curves. Select the pieces made up of 2 lines and delete them. Then use the Draw curve > Line command to draw in new lines, then use Edit > Join to glue it back together into one curve. You can skip the last join step if you want, the Extrude command will automatically join pieces together.

- Michael