the round things are not air bricks, but they might be another ineffective attempt to dry the wall.
If you pull up the carpet or vinyl, you should be able to see either floorboards, or concrete, or tiles. If you have a wooden floor, there will be a void underneath that needs to be ventilated. If it is solid concrete (or flagstones laid on earth) it does not need ventilation, but will tend to be damp.
The DPC (depending on the age of your house) will typically be a layer of slate between the courses of bricks, nine inches above where the ground level used to be when the house was built. Sometimes it is visible at a doorway. Unless you are on sloping ground, it is pretty sure to be at the same height all the way round the house, so once you have found it, you can work out where it will be when concealed.
It looks to me like you have three very common building defects
A cement plinth round the base of the wall, intended to prevent water penetration, but in fact prevents the wall drying out by evaporation from the bricks
A layer of black, probably bituminous, paint with the same intention but the same undesirable result
A concrete path or yard built against the house which probably is above the original ground level, which causes damp from the ground to soak into the wall; and prevents evaporation; and very likely covers the original DPC, thus causing damp.
Under no circumstances allow anybody who sells chemical injections near your house.
The corrective action would be first to strip off the cement plinth and expose the bricks. They may need patching and repointing as they were probably covered up to hide defects.
Then to work out where the original gound level and the original DPC are, and then most likely dig up the concrete and reduce the level back to the original (if this exposes the DPC then, combined with removng the plinth, it will probably remove the source of the damp)
When reinstating the ground next to the wall, it may be helpful to dig a trench and fill it with free-draining material such as cobbles or large pebbles. This is because water travels by capillarity through small pores. It travels most successfuly through very small pores such as bricks and soil, but cannot rise through the large gaps between cobbles. You could actually leave the trench open to maximise drying of the wall, but you might fall into it, so filling it with clean stones gives you a stable surface you can safely walk on. You can lay a drain at the bottom of this trench is the ground is unusually wet. Repair exposed brickwork as necessary.
I also recommend tht you look at all the drains, gullies and pipes around the house. If it was built before 1946, and is in or near a town, city, factory, railway station, factory, or canal, they are pretty sure to be cracked and leaking, which will add to your damp problems. Repairing them is not complicated and a local builder able to use a spade can do it. Try to find one by personal recommendation from someone you know and trust. listings on websites where builders pay to be shown are advertisements, not recommendations, no matter what misleading titles the websites use.