You can also step on one end of the bumper once you put it on the ground to make the other end stick up. Eventually you would phase that out.

Both are good suggestions. Progress slowly, inch by inch and day by day. The next hard one is convincing the dog that it can actually walk withe the bumper. They will retrieve it when thrown, but. Pick it up and walk with it.... It all comes togetjher in the end, but some take days/weeks longer for the light bulb to go on.

Good luck!