to do a leakdown test you would need a compressed air supply and a leakdown gauge. it is simply two gauges that measure how much air you put in and how much air escapes.
just do a compression test for the bank that's not firing correctly. if all four cylinders are comparable they should be ok. If one or two seem different you may have to do the other side to get your relative normal compression. Look for the cylinder that's different. (especially #7 if that is a continuous misfire) If everything looks ok maybe it's an injector not firing enough fuel. Spark, compression and fuel all have to work together to make the cylinder run correctly. Check all three.
If you have a scanner available check your O2 sensors
and also look at the misfire counter to see what cylinders are misfiring and how much they are misfiring.