You can't. Bipolar is an illness that 100% needs medical intervention.
Having said that, you know your own body and there are things you can do to help yourself if you are diagnosed as being bi polar.
Mainly of these are knowing when you need support and asking for it. You must monitor yourself and your feelings and try to be proactive (easier said than done) in attempting to control the symptoms.
Always have a circle of support around you ready, of trusted friends and your health and support workers and get it into your head that you CAN be helped and that help is just a text, message or phone call away. When you feel yourself sinking, immediately start talking and telling people how you are feeling so they can support and help you through.
Mental illnesses are killers and must never be underestimated and you CANNOT prevent them nor deal with them on your own.
If you even remotely suspect you or someone you know is suffering from a Mental illness, get some help. NOW
I know for a fact 100% that you can neither prevent or self treat it.
Hope this helps :-)