What tools would straighten the horn out?

Take or send the trumpet to a professional trumpet-repair place and only to
a professional trumpet-repair place. Check with the band department at
your local high-school to find out where they take or send their mangled
trumpets. A way to work within your two-day time frame might be to flop
down a couple of hundred bucks for a replacement instrument. Maybe you'll
be able to fool the kid's mother. Best of luck to you and to your
grandchild.

I googled for "trumpet bell repair" and got lots of hits.

Fill it with gun powder, add a long fuse. Place it outdoors far from
any buildings, light the fuse, and run like hell. When it blows, the
dent will be gone. Of course the whole trumpet may be gone too, but
that's the risk you take.