What can I do about this?

In theory, you could sue the manufacturer if you believe 1) that you used the product correctly (e.g. did apply too much or too often, or combine it with some other lotion, make up, etc. with which it reacted), 2) that the injury was not due to some sensitivity or allergy of yours, and 3) therefore, you believe the injury was due to a defect in the product.  It must be that the product had something wrong with it to cause the injury.
The reason I write "in theory," is that it may not be worth a lawsuit unless the scarring is significant and not likely to fade or you incurred very large out-of-pocket (not paid by insurance) medical costs. The reason for that is to sue you will need a medical expert to examine you, write a report and testify; and will also almost certainly need to hire a consumer product testing lab to test/analyze the deoderant and write a report (and have an employee testify at trial)--without these experts, you won't be able to prove your case or win. These are signficant costs (they could run several thousand dollars) which you most likely cannot recover in the lawsuit; as such, whatever amount of money you might win would be offset by your lawsuit expenses. Without significant injuries or medical costs, you could spend as much or more on the lawsuit than you would get back.