In order to escape Litwick Cave in Chapter 2, you will need to construct a pickax out of the materials found in the cave in order to make the crevice on the opposite side of the frozen Lake larger. By doing this, more wind will be able to enter the cave, which will then allow Drifblim to carry everyone to safety through the exit high above within the ceiling.
In order to create the pickax, you will need something sharp to work as the pick, something long to work as the handle, and a rope of sorts to hold the two together. At the entrance of the Cave, you will be able to Find a sharp rock that you can use as the pick part of the ax. You will also be able to find a wooden stick in this same General area, which you can use as the handle of the ax. After finding both of these, you can talk to Emilia to have her lend you her belt so you can use it to hold the rock and stick together.
After having all of the materials, go into you Case Notes and construct your makeshift pickax. After you do, head to the other side of the frozen Lake and make the crevice you Find larger in order for more wind to come through. After you do, return to Drifblim at the beginning of the Cave so it can carry everyone to safety.