By going to the source of all Truth: God Himself and ask Him. Not by going to sinners, or the recounts of sinners doings (aka history), or pedestaling men's logic, etc. By humbling asking God and listening His answer.
In my time studying Catholics, I noticed that many there use history-base epistemological approaches. I have a number of disagreements with that methodology, but for a thought experiment I did explore it for a while to better understand these believers. Honestly, using the same methodology I came to different results than the Catholics around me, but I still respect their conclusions/beliefs. Like I said earlier, my purpose of exploring Catholicism was not to be change my beliefs or to be prostylized too, but to better understand & love Catholic people.
Bytheway: Mary, would you mind acknowledging that you here my "no thank you to prostylizing" request? Just so I know the communication bridge is working.