To use Ascend, you’ll first need to select it as your primary ability by pressing and holding the L button to bring up the ability wheel and selecting the ability using the R analog. Once selected, press the L button again to enter Ascend mode.
Open ability wheel - Press and hold L button Ascend mode - L button while Ascend is selected as active ability
While in Ascend mode, he can look up and see a grid imposed on the ceiling above Link’s head. When the grid is green, Link can use the ability to swim up; otherwise, it will appear in red.
Pressing the A button while under an eligible roof will cause Link to swim through the material to the next surface that would allow him to stand up. When Link reaches the surface, he presses A again to get out of the ground. Pressing the B Button while Link is still on the ground will cause Link to swim back down to his original position.
Ascend - Press A button under an eligible ceiling Get out - Press A button while on the upper surface Go back - Press B button while on the upper surface or while swimming upwards
This ability can only be used upwards, so be sure to double check if you want to get out of the ground first, or find out if you have an alternate path back to your original position if necessary. Additionally, the ability has a cap on how high the ceiling can allow Link to reach; use the grid as an indicator, as it will only appear if the ceiling is low enough.