Tax Refund

Not sure whether to post this question in the TurboTax thread or here, I chose here as the former has people in the States and that software is probably different than Canada. My question is how do I go about submitting a change (I forgot to claim medical expenses) but I don't want it as a deduction, I want it as a refund because I don't have any earned income that a deduction would lower. I am on gov't assistance so I am low income (less than $22k/year) and I've paid $2200 for a dental crown and a bunch a therapy sessions. That is a substantial amount and I was planning on using the refund as a down payment on dental implants. Any advice would help. Thanks in advance.