First, prepare a mixture of dish soap and water, if the bubbles can't form it probably means that there isn't enough soap or that your soap isn't adequate.

Once prepared, gently blow facing the ring and a bubble should come out.

Enjoy :)

Printing Info:

• Use PETG or similar since it shouldn't be porous to water (like PLA)
• Use a exterior brim to hold the piece to the bed, otherwise the stem might have problems printing due to the low contact surface