That is really ugly customer service if you bought the boat new from the dealer 10 months ago, and upon having the D-ring patch separate on only its 3rd time being used, you are told by the manufacturer that it is normal wear and tear!
. That definitely is not
normal wear and tear! Hopefully the dealer stand behind what they are selling and do something for you, rather than just passing the buck along to the manufacturer.
As for the inflate/deflate question, have the boat fully inflated when you initially press the patch into place to ensure you have it positioned correctly. Then deflate it, and place the tube over a smooth solid surface with a bit of a curvature that is radiused similarly to the inflated tubes' shape. Use a roller to firmly press the patch against the tube, squeezing any air bubbles & wrinkles out the edges of the patch. The reinflate the tube and double check that everything is still properly positioned and that no patch edges are lifting away.
Be sure to use a 2 part glue that is appropriate to the type of boat fabric you have. Are your tubes hypalon or PVC? Also make sure that the D-ring patch is of the the same fabric type as the tubes.