Switch PhD program: how to contact possible PhD advisors when already enrolled in PhD program?
Email, honesty and avoid burning bridges.

You can freely email (and otherwise) contact potential PhD advisors, of course remembering that they are always busy, so you need to be concise and have something of interest to offer.

You need to be honest about your current situation. If you are not and then the potential new advisor finds out about it, it will look bad and will likely ruin your chances.

Do not quit your current situation. That would look worse than wanting to change/improve your circumstances. And if you fail to find a new position, you'll be left with nothing.