ENGAA and TMUA helpWatch
For the ENGAA, going from a 3 to 6 would be pretty hard to do in a week but not impossible ig. First of all, go through the specification and make sure you're solid on everything. Especially, energy conservation and topics like waves: I've noticed they like to use those topics. From there, there's not much you can yo asides from practice papers (under timed conditions of course). You can use each paper more than once.