Using the UBT-12HC Serial Bus Motor with Arduino
You can find various libraries on GitHub - search for UBTech or Alpha-1 or UBT-12HC, or JIMU.  It looks like a very old UBT-12. Current versions have and internal color changing LED.   The protocol is 10 bytes long, starting with a header 0xFA 0xAF then the servo ID, then the command byte, then 4 data bytes, followed by a checksum, and a 0xED ender.  Don't try random commands, as you can easily brick the servo. Communication is 115200 baud, single wire, bi-directional.  I use an 74LS126 to drive it off any 3.3v controller, such as an arduino, raspberry pi or pico, etc.
 FA AF id cmd d0 d1 d2 d3 cksm ED

 example: move to position 90º ( range is 0 to 240 ) medium speed

 id   depends on the servo, can be 0 to 253
 cmd  0x01
 d0   angle  90 decimal is 0x5A hex
 d1   speed, in 20ms time chunks, 0 is fastest
 d2   0
 d3   save as d1. 
 cksm add bytes starting with id and ending with d3, modulus 256

 FA AF id 01 5A 25 0 25 ?? ED   # note: cksm depends on id

All UBTech servos use the same protocol.
Unfortunately it's getting difficult to find UBT-12HC servos, and the company isn't helpful with documentation.
Oh, and the board you bought is for a similar servo, the LX-15d or LX-16A (and others) made by LewanSoul or HiWonder.  DIFFERENT POWER PINS !!  and a different protocol.  Much better servos, still being made, and lots of documentation.  You can save yourself LOTS of trouble by just buying LX servos.
good luck!