Use Fux Capacity Checkpoint

https://civitai.com/models/679262/fux-capacity-nsfwporn-flux-base-model

Trigger words

upskirt
pussy
shot from below
lift skirt

Additional trigger words that can help the concept:

lifting skirt

Lower the weight of the model to make the skirt lifting more subtle. ~0.7 - 0.8 for a subtle peek (depending on prompt of course).