For this achievement you need win a Ranked Deathmatch game with at least one Worm on over 100 health at the end (any map).
Simply wait until a health crate drops and collect it with one of your Worms. This will give him +25 health. Make sure to win the ranked deathmatch game and prevent this Worm from taking too much damage.
If you're having trouble getting this legit you can try to boost it. The only problem with boosting is that ranked online matches can't be limited to 2 players / 1vs1. Every lobby has room for 4 players. But as soon as 2 players are in the same lobby a 25 sec. countdown will start. If noone else joins in the meantime the game will start with only 2 players. Skip turns until the health crate drops and whoever is going for the achievement must collect it. Then the