The fill command won't replace beds, as shown by the images below. This does not work in command blocks either. Actually I'm just dumb and put the command in wrong lol
MCPE-146101
Fixed
Resolved
Invalid
0
The command you put in is wrong. you put in ~5 ~5 ~5 ~5 ~5 ~5 which means from +5 blocks from current location in x y and z to +5 blocks from current location in x y and z.
Try /Fill ~-5 ~-5 ~-5 ~5 ~5 ~5 air 0 replace bed.