For the MCAT, you are not expected to know how to reduce carboxylic acids to aldehyde. For some reason, this step in terms of a 1-step reaction is a bit more complicated so therefore, its not an expectation that you know it.
Based on what you do know right now however, you could reduce carboxylic acids all the way to alcohol, then oxidize it to an aldehyde (LiAlH4, then PCC).
I hope that is helpful!