The the cooling system is self venting via the expansion tank cap, there are no venting plugs only filling points one in on the thermostat housing the other on top of the rad, but you can get an air lock when refilling the engine with fresh coolent.
To prevent air locks which usually happen in the heater matrix but also can be in the engine and which will reduce the coolent flow around the engine (not what you want) fill both the thermostat housing and the rad, and when free from emerging bubbles, replace the plugs.
Turn the heater controls to hot and leaving the expansion cap off start the engine, if you bhave any air in the system then you will see bubbles rising, when that stops replace the cap and stop the engine and let the engine cool, then check your coolent level again.