It's right there in the title. How to do it is, of course, the dilemma. You need a teacher and you need to carefully follow explicit directions. If either are missing, don't try. Just stop chasing esoteric experiences. You have been warned.
After you have a bit of stillness, gaps in the sensorium can be addressed, over time. Light yi begets mild qi. As these gaps fill, naturally, over time, using light yi, the dantien will fill with softness, not pressure or heavy power, but lightly. From this lightness the qi will suggest that you let it condense. It wants to condense and move. Do not interfere with this process. Over time, notice how important the time becomes. It take time and consistency, not desire or want.
The interference itself is the challenge. Is your mind clear and stable? Are you light enough? Do you have the required physical capacity to actually succeed? Yeah, FAFO. Find a teacher who has an explicit method.
