I will give this a shot, though explaining 3-D concepts in writing is not my strong suit, however I have a good deal of experience using epoxy to repair damage to wood. Cut a piece of thin plastic the width of the sound hole and tape it snugly to the underside of the damaged blade so that it comes forward into the sound hole. Mix your epoxy with lightweight filler. You can use wood dust if you have a suitable color match. When it is the consistency of peanut butter, apply it to the damaged area, building up the damaged edge. Once the epoxy has cured, you can un-tape the plastic strip and gently pull it away from the underside of the blade. Since epoxy will not bond to plastic, the strip will release from the cured epoxy. You can then proceed to file down the repaired portion until you are satisfied with the results, testing the sound as you go. If you don’t have experience with these types of repairs, I would suggest testing out the mixing and application on a scrap piece of wood to get a feel for it. The advantage of this type of repair is that you can maintain the original voicing, whereas adding thickness to the underside of the blade can change tone and volume. Best of luck.
Anybody interested in a trade for the instrument pictured above. It needs work on the blade as mentioned. I have a lot of projects underway and it’s not a priority right now. I would suggest sending it to a recorder tech or whistle maker for a look.
The plus is that it plays in c (c is the bell note which is rather rare) at 440.
I’m interested in a good B whistle or maybe a Killarney D. Or piccolos and anything boxwood.
Also have other whistles and flutes around to sweeten deals or whatever.