It sounds like a simple round over bit would work but I am not sure what you are asking from your description. Can you tell us more about what you mean by the rounded edge being 7mm?
Thank you all for your replies. I have a 1/4 inch freehand router and a 1/2 inch table mounted router.
The total size is less than 1 metre.
26.5cm deep x 10cm wide x 21mm thickness
It needs to be rounded on two sides like in this image (red represents rounding)
The rounding needs to be done in the same way a window board is rounded.
I don't think there is a bit supplier close to me and I cannot take a profile from the existing as it is from the top of a step profile. I expect that it was made in 1958, so you are spot on!