Is the transformer marked with "primary" and "secondary"?
Transformers are kind of dumb in that they simply step up, step down, or simply isolate having a simple 1:1 ratio.
The 240v side of your transformer should be marked with X1, X2, and X3. The 480Y/277 should be marked with H1, H2, H3, and H0.
Based upon the minimal infirmation privded in your post to use this transformer simply bring our 480, 3ph, 3w with the EGC. Terminating on H1, H2, H3, bonding the EGC to the enclosure. Leave the H0 insulated and isolated.
Connect you 240v to the 220v load. The problem that you may have is if you need to ground the 240v side. Since ther is no neutral as with a wye you may have no other options other than to corner groung it as in a grounded 'B' phase.
Depending upon the actual secondary voltage you end up with you may not need to make any voltage adjustments. If you do there should be taps provided of the 240v side which are commonly labeled a +(2)2-1/2% taps above normal and (2) or (4)2-1/2% taps below normal.
The name plate is commonly maked with the tap voltages 252, 246, 240, 234, 228, and is (4) below taps are included 222, and 216. In a normal application where you would be using this transformer to step-up you would select the tap that has the closest voltage to that which is being supplied to assure the you would have close to the desired 480v out.
When using this transformer as a step-down you can use these taps to adjust the output voltage to 220v but it would be dependent upon what the actual supply voltage is and if there are sufficient taps available to abtain the desired output voltage