You may use adjustable Voltage DC-DC converter such as LM2576-ADJ, LM2596-adj , play with NTC + Divider Resistor at feedback you may get it
https://www.ti.com/lit/ds/symlink/lm2576.pdf?ts=1679379636858&ref_url=https%3A%2F%2Fwww.google.com%2F
This inductor is made using POT Core, value Approx. 640uH to 680uH will work, current could be 100mA,
you may try Drum Core Coil from Mouser Part No 80-SBCP-80HY681H
https://www.mouser.in/ProductDetail/KEMET/SBCP-80HY681H?qs=pfd5qewlna7zBsC5r9mWjg%3D%3D
Or you may make one using POT Core...