you can't edit a bitmap in flash.
you can draw/paint over the bitmap (use a different layer above the bitmap's layer).
and you can convert the bitmap to a vector (modify>bitmap>trace bitmap) in flash then then edit the vector.
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If you do want to edit the bitmap itself, you can right-click on it, and select Edit in Adobe Photoshop. In Photoshop you make any changes and do a Save. The version back in Flash Pro will then update.
That has worked but it smudges the work.
Is there any other way than trace to get it edited on?
if you want to edit the bitmap, you need to use a bitmap editor. as colin suggest, ps is the go-to program for bitmap editing.
that said, by changing the trace bitmap settings you can get pixel-perfect rendition of that bitmap into a vector editable in flash. experiment with those settings and the undo shortcut until you get what you want.
gradually increase the settings to find what you want. these are almost always (for me) unacceptable:
anything more than this and flash may not be able to handle it. and using these settings you have to look carefully to see a difference between the bitmap and vector.
the one on the right is the bitmap: