see links in this page https://docs.m5stack.com/en/unit/gps
there is the datasheet and commands are in another document "CASIC Multimode satellite navigation receiver protocol specification", google can translate pdf from Chinese to English quite well.
Also manufacturer has agps example on their web (when it works, now it doesn't for me)
same chip is in B5 fitness tracker , I tested few commands listed here
when the tracker arrived it had only gps and bds enabled, there is PCAS04 command to enable any combination of gps,glonass,bds and enabling glonass worked.
except setting refresh via PCAS02 I did not find any command to put it into some power saving mode as mentioned briefly in datasheet.