I actually really used to love the OZ *A search tool on their Korean website for the fact that you could input flights segment by segment. As some have mentioned the lack of a calendar function could make it a little tedious but you could search individual non-stop flights on another *A website and them piece them all together on OZ's website. Any other airline and you would have to call in and feed the phone agent flight numbers one by one. At least that was the case back in Dec. 2020 when I managed to book myself a mixed class, multi-day itinerary from SIN-NRT-ORD in J and F. Nowadays it looks like you can still search segment by segment to confirm award space but have to call in to actually book the ticket :/