You don't. It is a 3.3V device which CAN be powered by 5V (often USB).
If you have low power 5V devices you can power from the VBUS or VSYS pins which can be used for power if you run the Pico from 5V.
VBUS is the micro-USB input voltage, connected to micro-USB port pin 1. This is nominally 5 V (or 0 V if the USB is not connected or not powered).
VSYS is the main system input voltage, which can vary in the allowed range 1.8 V to 5.5 V, and which is used by the on-board SMPS (switch mode power supply) to generate the 3.3 V for the RP2040 and its GPIO.
The Pico Schematic is in Appendix B: Raspberry Pi Pico Datasheet