1. Please read the advertisement and or recruitment Rules of the new job to get help on the steps to be taken In such cases it is the Rules and not the convenience of the applicant which matters.
2. If it is permissible in your new employment then it is always possible for you to resign from your previous employment for get confirmation of the new employment.
3. Without having read the recruitment advertisement or the recruitment rules, if any, none of the questions of your query can be effectively answered.