How do I reduce the frequency of electric current for part of a circuit that has variable frequencies?
Having read through all the comments and the question I would consider using a phase locked loop (PLL) circuit that has upper and lower limits of 240 kHz and 220 kHz. The PLL would then produce a DC output voltage that was directly related to the frequency of the signal between these two limits. This technique is called frequency demodulation.

I think the LM565 would prove quite suitable as a frequency demodulator as it operates up to 300 kHz: -



If you find it hard getting that chip the 74HC4046 PLL is available.

To turn that DC voltage (the PLL output) to audio requires a simple voltage controlled oscillator circuit such as this: -



Virtually any op-amp would work in the above circuit