from another forum re same issue ...
Another method is take some sticky tape, press in onto the dust cap just enough to get it to stick, and then pull gentle on the tape piece pulling the dust cap back out. Sometimes you may have to do it more than once to get it all out. I've done this for friend's speakers with kids and had it work very well
I suggest not using a regular vacuum cleaner, but a dust buster type of device with a crevice extension tool attached. Much lower suction power, but enough to bring your woofers dust cover back to it's original shape. FWIW the inverted dust cover will not affect frequency response. It is there as the name implies, to keep dust from getting into the gap
decided to try the duct tape method. FWIW, these dust covers are paper, not poly. I tore off a piece of about 1" by 1" and lightly pressed it into the middle of the first cover. Waited about 5 seconds and pulled it off - nothing. I figured that dear Hannah had just pushed these suckers in too far to be brought back out. Then I tried a bigger piece, covering the whole dust cover and I think this is the key in my case: lightly traced the outline of the pushed in area with a ball point pen, and waited about 15 seconds - I think allowing the extra time for the tape adhesive to make contact with the paper cone cover. Gently but quickly pulled the tape off, and WTFDYK --a good portion of the pushed in area came out !. I repeated this about 3 times for each speaker and both covers are now popped out. The only negative is that the adhesive left a darker shade of black paper where it sat over the damage, but at least the cone is popped back out. I have now gone and found the original speaker grills and put them back on. My advice is to try the duct-tape method before resorting to the less easily controlled wind vortex properites of your trusty Hoover or Dyson