How can I find my clan which I had left? I also don't know anything about that clan . I just only know the name and I search too long.
https://www.clashofstats.com/ keeps track of player's Clan history. If you look up yourself, odds are they know in which clan you were... If it was only for a very short period however, they might have missed it.
Unfortunately, you're going to have to keep searching. There is no way to see which clans you were previously in. The only way you'll be able to find them is by searching through the Clan Search page and scrolling through until you find it. If you really only remember the name, you might be out of luck. The more information you have for the search the easier it'll be to find them. Best of luck!