Only in series, never in parallel. Not to overload the amplifier and avoid damaging it; taking care of the polarity: unite negative of one to the positive of the other, leaving extremes + and -. It will have less volume, but only a little. This assuming that both speakers are normal and balance control centered. Greetings.
The cop partner told you very clearly, let's see you have 4 positive and 2 negative connectors, connect a positive with a negative and put an insulating tape, you have 2 connectors, one positive and one negative, connect them to the equipment at the output that works the positive in the positive and the negative in the negative