This is common with many cups and is a result that differs person to person and cup to cup.  Below are a few things that you can try.
Pinch the base of the cup several times in different areas.
Pinch the base of the cup and rock it side to side.
Insert a finger and gently press the side of the cup moving in different areas.
Wiggle the cup down until the rim opens and then use a finger to push it back into position.
Insert a finger and “swipe” the cup.
Insert a finger, press the body of the cup to your vaginal wall, and then slow release the pressure allowing the cup to open against your finger.
Please visit our troubleshooting page for more info and tips!