Dry ice it then heat it.

if you try heat you risk making the stainless brittle and headers are anealed a form of stress relieving after welding
i dont recommend it as a metal man if you do decide to use heat do not heat past the metal being golden umber in color anything past that leaches the nickle and chromium out of the stainless
releasing all of the metals inherent properties
you might try drilling a very small hole and using a self tapping screw to pull the dent out
then tig weld the holes closed
purge the inside of the tube being welded with pure argon
then pressure test the weld with water not air to see if its sound
no matter how you slice unless you have the capacity to do the work yourself its going to be expensive
good luck
PS WJB21 also had a GOOD IDEA even better than mine tig a rod on and use the rod as a slide hammer
no welding needed mind the heat though, thats still valid might even work without the extra heat

I would call CMI or email them the picture and get a price.

Good luck with that. $5 says they'll tell you that can't fix it. That is, if they ever call you back. They are the worst company I've dealt with.

C. deezy was right about slice and weld. Been there,done it.

+1 your best bet for the least noticeable repair is going to be with a skilled welder/fab guy. I wouldn't cut out the entire tube though, just a window where the damage is in a rectangle. I would use the thinnest cutting wheel i could get my hands on, even one of those Dremmels if need be they have some really thin wheels and you would go through a bunch. Once the piece is cut free metal finish the dent out and weld it back in. I use to do high end sheet metal fab for street rods and vintage restorations and this method really isnt that much of a stretch. I highly talented welder could tig that back in no prob and once finished out at worst you might have a slightly discolored surface that you would really have to point out to notice. Hell if i was a better stainless welder I'd tackle this one just for fun

stud gunning it (the method of welding the rod on) is pretty specific to very small dents and can work but these look a little large for that. The problem is it will sort of stretch and pyramid the metal on larger dents making the surface even worse. Dents do not "pop" out when trying to repair them, the metal has to be worked back to its original shape. The metal has been stretched to form the dent and stud gunning can stretch it even further.

Are we looking at two dents on that tube, one by the seam and another further down the bend?

Send them back to CMI they can fix them and the work will be correct,we just had some sport tubes fixed with dents and they look like new now 2c