How to set timing on CF172MM(250CC) Water Cooled Engine (304-999019)

a SCOOTER. year 2000. not cc (LOL)
cloned version of Honda's AF18E/AF16E Dio motor.
Air cooled, 49cc, single cylinder, 2-stroke
Compression Ratio: 7.2:1

it's in the manual. RTM" service manual

there is computer model to calc, this using compression ratio and cylinder volume
but
here is generic list.
my lawn mower is 100psi;. (and mopeds and outboard tiny motors and scooters tiny not 250cc hog scooters)
my old car is 150psi
my newer car with high 10:1 CR , is 200psi
a 49cc engine 7.2 CR is like 80psi.
low and expected. at that CR, 100 max
to get the reading correctly
good guage
fast cranked (kicked or starter turned)
let the meter peak and peak is spec. read peak PSI
and the CR is what matters.
and only on a warm engine, warm/hot not cold
cold is way less.
when warm the rings seat, cold they do not.(well)

Oil is pumped around the engine. If there is water in the oil, that too is pumped around the engine.
If the engine is water cooled, I would remove the head, if it is warped, have it skimmed and then refit with a new gasket.
If it is air cooled, condensation is common. Replace the oil and any filter.

Free service manual if that is what you need:

https://www.carlsalter.com/download.asp?p=2074

That is the engine default code. It has to do with the regulator not getting enough water to cool it down. Those are water cooled regulators not air cooled like cars. The impellers for the cooling system should be replaced about every 3-4 years. It may still cool the motor but not enough to cool the regulator which supplies the computer to set the trouble codes.

engineering standards say around .012" inlet hot and .014" exhaust hot ( air cooled engine )
lowest setting would be .010" hot inlet and .012" hot exhaust ( air cooled or water cooled )
get the exact settings from a mower shop

Does the engine have a cowl cover? If so it is water cooled, the water is pulled in down by the propeller shaft. If the engine is open no cowl and block and head cooling fins then it is air cooled.

water cooled engine .010" hot inlet and .012:hot exhaust. If air cooled go up .002" on the settings.

if its water cooled the head gasket has blown

if you contact fowlers of bristol and give them those part numbers they should tell you what bike it is from

Your bike has electronic ignition. There is nothing to set or reset on the timing. Change the spark plugs, adjust the valve lash, change engine oil and filter, clean or replace the air filter, lube and adjust the chain and cables, inspect the sprockets and wheels, add water to the battery if needed, wash the bike. That's pretty much everything the dealer does.