I live in Karachi, Pakistan and I have got a job offer from Dallas, Texas, USA. I am likely to move their soon. While researching the cultural difference I realized that a bidet is not usually used in USA and people prefer just the toilet paper. How should I ask my co-workers to install a handshower inside the toilet?
Use a portable bidet like one of these. I keep one on my boat for overnight trips.
Your coworkers never need to know.
I worked with a Pakistani in my last job, I'm reasonably certain this is what he did judging by the parcel he carried into the toilet occasionally (presumably when #2 was imminent). He carried a prayer rug in a similar parcel when he used an empty office for his prayers.
If this is a medical condition which means that you need this facility, then you bring it up with your manager or HR, not with your co-workers.
If it's actually not a need but a personal preference, then I'd strongly suggest that you don't bring it up at all. You made the decision to move to a different culture, so a lot of the burden is on you to adapt to that new culture, not on that culture to adapt to you. Otherwise you're saying "I'm special. You all need to change your life because I won't change mine.", and that's not a way to fit in to a new culture, either at work or outside work.