There is a flat edge opposite the entrance (close to where you got the Health Potion earlier). Hang from there.

Release three times to grab the lower handhold. The last drop is a long one, so press the Interact button to save Lara. This handhold is about to collapse, so quickly traverse to the right around the two corners. Remember: to move faster, tap the Interact button along with the direction key.

Jump to grab the handhold of the next pillar on the right.

Again, the handhold will soon collapse, so quickly jump to land on the safe rock ledge on the right.