basic answer is that it is doubtful to convert one of the existing outlets. You need to be semi competent with house wiring to try to wire a hot tub to the national electric code by yourself.
If you understand things like nec, gfci, nm-b, nm-c, uf, thhn, thwn, 110, 220, disconnect, 10/3 w/g, difference between grounded and grounding, etc. then we can talk further about it.
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