How much transmission fluid does the transmission in a 1999 suzuki swift hold?

First thing I would do is get the transmission fluid changed and make sure the transmission fluid is at the full level. If it still slips, the clutch plates are probably worn and need replacing. That would be a transmission rebuild.

https://www.autodoc.co.uk/car-parts/gearbox-oil-and-transmission-oil-11915/suzuki/swift/year-2007

what transmission
stick or auto, we can guess,
if auto shift to neutral and try now.
battery lugs green, with corrosion clean them
jump start it? yet.
head lights bright? y/n

Drain plugs are situated on the bottom of the transmission - usually on a lip/corner. The link below shows generic images of drain plugs - which my be an 8mm square recess plug, hexagonal recess or even a nut/plug.
auto transmission drain plug Google Search

The filler plug will be higher up. Again, it can be an 8mm square recessed plug, hexagonal or..

You can refill the transmission via the transmission dipstick tube.

It should be oil....but it is easy to figure out what it may be by its color.obviously fresh oil is amber to brown...dirty oil is almost black.
transmission fluid in automatics should be a shade of red. Clutch and brake fluid light yellow.

welcome to a USA forum where we dont have 09 swifts, nor any books on it.at all.

the tranny is sick if fluid levels are full, and clean and filter clean.
get it serviced.

Have the vehicle code scanned. Could be many things like faulty TCC solenoid or bad torque converter, could be low on transmission fluid. Could also have faulty shift solenoid or VSS sensor.

what tranny? A/T or M/T we can not guess.?
what country helps too.?

bad shifter linkage, or adjustments.
or bad transmission.
I do this test off road.
the acid test.
i remove the linkage, and then shift to 2nd.
drive car, if it holds the gear, the tranny is good.
simple , huh? but is dangerous, do so only off road.
far from other vehicles or people of any kind.

if you cant do that , then fully inspect the linkage and RTM
read the fsm for your car.

should take dexcron...call your local parts store & they can let you know also. this info should also be on the dipstick.

If you are talking about the brake fluid reservoir, you need to use brake fluid. Not oil.