Know your output from your mixer: is it balanced (mono TRS or XLR) or unbalanced (RCA or TS or stereo TRS).
Then look at what is at the club on the connection side. You can go unbalanced to unbalanced or balanced to balanced, but do not mix. If you stay with the same signal type you might just need adapters or the right cables.
If in doubt, take pictures of the club equipment panels (note the make and model too) and we can help you if you are still struggling.
if you’re going to set up more speakers, you’re going to need another amp, as the one already in the club is probably only big enough to power the two speakers in there. my advice is: if you’re going to bring in a system, don’t use their system. it eliminates a lot of headaches.