I entered an airway, UM677, but the route I had did not work on this airway. So now do I now remove the UM677 in the airway on the fmc route page? I press delete then highlight it nothing.

Just enter the airway/route you want below after UM677.

You might have to enter the first waypoint of that new airway/route as a "direct to" waypoint first!

You will get a route discontinuity.

 

Then put the beginning of that new airway/route in the right sequence on the route or oegs page.

 

execute.

 

The idea is to overwrite your previous entry with a new waypoint that is part of your required route (rather than trying to delet UM677)

Thanks, the overwrite previous entry with next waypoint is a great tip.