How to study Step 3 for old IMG graduates !

Hi, I am old IMG who took USMLE step 1, 2, CS and ECFMG certified 15 year ago (in 2005) and returned home after failed match. I did MD in radiology and doing good. Now, I want to do fellowship in the US and they says "Step 3" is must.

I'm pretty much determined to sit for Step 3 and can spare 4 to 5 hours daily for studying MLE.
My questions:

1. What to study for Step 3 since my basic (Step 1) is almost zero present and how important is Step 1 in context of Step 3 ?

2. How to study, how...

How to study Step 3 for old IMG graduates !