I’m an Alchemist Who Doesn’t Know How OP I Am is a Manga/Manhwa/Manhua in english language, Shounen series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

In order to save her little sister's life, S-ranked adventurer Laffey seeks an all-healing elixir. However, elixirs are highly precious items that take years to make by even the most experienced of alchemists. But one day, she meets a man that defies these rules! "Here, an elixir. Oh it's fine, I can always just make more." A slow-paced fantasy about an extraordinary alchemist who doesn't know his own strength and the beautiful adventurer who gets caught up in his efforts to help others!