This throw, at first glance, looks similar to De-Ashi-Barai. Both are ashi-waza (footsweeps), but in De-Ashi-Barai you sweep one foot, and in Okuri-ashi-barai you sweep both feet.
Use Tsubame Gaeshi to counter sweep an Okuri-Ashi-Barai. First you must read your partner’s attack. Anticipate the movement. As they go to sweep, lift your foot clear by bending at the knee. Now continue the movement and counter-attack. Tsubame Gaeshi is not a technique in the official 40 throws of the Gokyo, but it is in the Shimmeisho no waza.
All ashi-waza are great for setting your opponent up for a follow up technique because they create a big reaction from your partner and this movement is what you are after. Use Okuri-ashi-barai to set up for Osoto-Gari.