Can i use a stepper machine if i have plantar fasciitis (on left foot)? or will it cause more damage?

Depends. If you seek out and obtain proper arch support that can eliminate the stress on your feet, you can do whatever you want. If not, any activity that involves stepping/walking can aggravate this process.

It would be prudent to consult a podiatrist and have it treated. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines