[DjAlamose]

It’s easier to make a whole new part for this one...
Or you can try making it in as a sheet metal part, but I don't know how exact you are going to be able to make it.

But! This is how I would do it:
Measure the length of the outside and inside arcs. Make two concentric arcs in a new part file and then spread them apart so the distance between the two arcs is the width of the channel. Then constrain the arcs so their length is the same as those measured. Inventor has some strange constraints so try a few things before you actually make the part. Then you should be able to extrude it and vwala, you have your part!

I have no clue how well this would work until I actually tried it, but this would be my first choice.

And if you can’t find the measurements or the arc length then could you post the radius and height difference all I can get back to you on how long they are.