Hmm, if it does not have built in effects that you are looking for, you could hook the audio output (if it has one) through something like a guitar effects pedal and then hook that to an external speaker. There may be other ways to get the same result using specific MIDI hardware.

Also, if you can provide the make and model number of your keyboard/organ, that would help out.

I think you mean a VST effect upon your organ, download Chainer VST host install. Go to KVR audio search for free VST effects.
The effects are modelled by your computer, if you have an ASIO audiocard "if not you will have to install ASIO4ALL" to get VST working you must put your audio card line in as input. And of course a cable from organ "head phone/line out" to computer line in.

Then select input in chainer, and open the effect.
It is a rather long description to get it up, and you must set up audio inputs in Chainer, and put the VST effect you download into correct folder.
You can of course use any electrical bass/guitar or analog instrument to do the same thing as long it has a microphone connected to mic in on computer.

I am sure people help you put it up.
And it does not have to be Chainer, you could use a DAW or any VST host to do this.
It could be that SAVI host is an easier choice.

https://www.hermannseib.com/english/savihost.htm

If you intend to record on the fly you should probably use "Reaper" as your VST Host.
It is not free and have a snag screen you have to wait for complete though.

What softsynths/organs do you use now, are they standalone or in a DAW digital audio workstation?