first off, read your manual.
Generally*, subs that require speaker level outputs are part of an "all-in-one" HTIB system and are usable only with that (or a similar) system.
If, in fact, this subwoofer was included in the same HTIB package as the receiver, I guarantee the receiver WILL have a speaker level output to drive that subwoofer. You must find and use that.
But, if you went out and purchased a standalone receiver and a separate "all-in-one" speaker package or a "passive" sub, all bets are off. The receiver will most likely not have speaker level subwoofer outputs. I cannot think of one that does. They all use those RCA connectors, which need a powered subwofer.
You need to use a powered subwoofer, or a separate amplifier for the subwoofer.
*Yes, there are some fine upscale subs that are "passive", but it's understood up front that they require a separate amp to drive them.