Well, Deku does lose his quirk. However, this event leads to new developments and challenges for him. It's a crucial plot twist that adds depth to the story.
In many fanfictions, Izuku might unlock his quirk through intense emotional experiences. For example, a moment of extreme anger or determination could trigger it. Maybe seeing his friends in great danger and feeling a strong need to protect them could be the catalyst.
In some fanfiction, Izuku also experiments with different environments to cultivate his quirk. If his quirk is related to strength, he might try training in places with different gravitational forces. This forces his body and quirk to adapt, and in the process, he can discover new ways to use and develop his quirk.