I would let both know that your in need of that service just to be on the safe side....
You usually have to put a request when booking or check-in. When you check-in for your flight look for the option of wheel chair/special assistance required. I beleive thus then makes the airline the concerned party. Other wise when you go to the airport let someone at the ticketing counter of respective airline know that you need assistance they would then provide it.
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