My baby is 4 months and have not flipped yet, how do I help her flip?

I give my baby a help. I will help her turn and lay down for tummy time. (So she will have a feel of this is flipping/turning) No1, i let it naturally, hence everything is slow. No2, i give a helping hand, he is learning everything fast. (Anyway, just a matter of time, when they will flip, by 6 months, they are quite strong and will be able to flip here and there. Just be gentle, it's like when you lay her down and carried her and turn over for tummy time on you. (It's about the same but on bed)