I looked into it, but it's so complicated, I haven't worked it all out yet.
I checked it out, but it's quite complex, I haven't figured it out completely.
この場合、次のような言い方ができるかと思います。
ーI looked into it, but it's so complicated, I haven't worked it all out yet.
「それについて調べてみたが、複雑すぎてまだわからない」
to work out で「問題などの答えがきちんと出る」
ーI checked it out, but it's quite complex, I haven't figured it out completely.
「それについて調べてみたが、複雑すぎてまだ完全にはわからない」
to figure out で「答えを見つけ出す」
ご参考まで!