If you are referring to the repeat previous measure, it is %

You should see the key commands in the various menus (to the right of the menu action).

Repeat barlines
For repeat barlines, Edit > Insert > Barlines
There is one for opening and another for closing repeat barlines.

If you are using the arrows to navigate through the chords then need to correct one, just start typing, for instance changing a chord to F7, arrow to the incorrect chord, then type f then 7 then the Return key to enter it and move to the next space.
Does this work for you?