A few possibilities:
- unsolder the 5v regulator and put in its place a 3.3v regulator of the same form factor;
- the schematic suggests board space for a mc33269st but doesnt have the actual part in. in its space, solder in a 3.3v regulator and unsolder the 5v regulators output pin.
- if you already have a 3.3v source, jump the 5v regulator's input/output pin, and plug in the 3.3v source.
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