Just try hard!
You need to do the bleep test only at OASC, you need to pass the level for your age but you will get extra board points if you do well so DO NOT STOP until you genuinely can't do anymore - an extra board point or 2 may make all the difference if you are borderline or trying to join a branch with stiff competition. There is loads on web about the OASC process, jst google it. And recruiting figures are doubling in the coming financial year