They continued along the tunnel until they reached another trapdoor where Yinn had taken the initiative to climb up the ladder. She purposefully knocked twice and waited for a response knock.
What they heard in return was some sort of morse code. While Jin knew the basis of morse code, he needed time to decipher it and it was even harder without the System to identify it for him. And yet, the former astral cultivator also believed that it was useless to even think that morse code could be replicated the same way as what he had on Earth. So, he stood at the side waiting for Yinn to give the affirmation morse code. (Author's note: Nope, no peeking up!)
Yinn replied in response and soon the trapdoor opened, beaming in stronger rays of light into the tunnel with words of relief being thrown towards Yinn as she reunited with the group on the surface. Jin climbed up slowly and noticed that the chattering ceased slowly with Yinn leading the squad to be at attention.