Your supervisor needs to support you after submission. Your supervisor is also probably really busy. The best way to get what you need from them is to be as specific and clear as possible.
Before submission, think about what you might need. A mock viva? General support or questions around particular parts of your research? Insight into examiners or the viva process? Explore what you might need before approaching your supervisor.
Before submission, ask about their schedule. When are they busy? Do they have times where they will be unavailable or less able to help? Find out what could get in the way of you accessing their support.
After submission, ask for help as clearly as you can and with as much notice as you can manage. Be specific in your requests, so your supervisor can respond and match your expectations as closely as possible. There may not be time to get everything you need, so consider what your priorities are and communicate them.
You need help from your supervisor to help you get ready for your viva. Support them and they can support you.