Hi,
I program the fuses few day ago... Good starting point is to read IMXULRM (fusemap, system boot, and on-chip OTP Controller) and AN4581
then you can program fuse from u-boot command prompt: fuse prog <bank> <word> <value> - this is permanent.
(how to build u-boot - you can find in i.MX6UL hab_status )
you can also normal boot into kernel, go to /sys/fsl_opt and echo <value> > HW_OCOTP_...
Regards,
Robert