how to run three subs from one lfe jack

If your receiver had a single sub output, it implies that it does not have the provision to do bass management of 3 subs.

Get a miniDSP 2x4 HD for the subs, if you care about the sound quality and more granular control. If the restaurant has 3 improperly setup pounding beasts, customers may jet quickly.

1. Not interested
2. In bass managementhe receiver will roll off thelows the subs are to fill out the freq response of small speakers as long as there’s some bass everyone is happy

@mashif is correct. Just get subs you can daisy chain.

Can't need to use a particular su and daisy chaining may not wok logistically 

You can put a couple of these together and create more outputs from the receiver.

https://www.transparentcable.com/products/rca-y