Current Native Call Recording CSC for Samsung are as follows;
Bangladesh (BNG) Call only
Thailand (CAM/MYM/THL) Call + SPay
Egypt (EGY) Call only
Israel (ILO) Call only
Laos (LAO) Call only
Libya (BTC/LYS) Call only
Nepal (NPL) Call only
Sri Lanka (SLK) Call only
Allergy (TMC/WTL) Call only...
Unfortunately you can't flash a boot loader from a different version, so the U1 has to stay a U1, B has to stay a B. Since the U1 is just sold in the US, unless one of the carriers unlocks eSIM or Call Recording, changing the CSC is useless.
Download Odin 3.14.1
Download SM-F926B_XID_F926BXXU1AUG8 from your favourite firmware download site
Flash AP/BL/CP/CSC using ODIN, make sure for CSC you load the CSC_OMC_OLE and NOT the HOME_CSC
XID version enables call recording and e-SIM on your SM-F926B/DS