If you, for example, want to change the dirty air for Red Bull, you have to change the XML file in C:\Program Files (x86)\Steam\steamapps\common\F1 23\2023_asset_groups\f1_2023_vehicle_package\teams\redbull\wep\redbull.erp. (redbull!!!temp000.vtf, extractable with EGO ERP Archiver 9.1.0). The part in <F1Aero></f1Aero contains the values for dirty air, DRS, etc.
You are looking for these 3 lines:
XML:
<m_aeroSlipStreamAirDensityScaleLift value="0.88" />
<m_aeroSlipStreamAirDensityScaleDrag value="0.83" />
<m_aeroSlipStreamCarWidth value="1.5" />
The first line is how much the car in front helps you because of the slipstream effect. It increases your speed if the value is below 1.
The second line causes the car to lose drag because of dirty air. A value below 1 causes the car to lose drag (increase aerodynamic resistance). A value below 1 decreases your speed and handling.
The third line states how thick the line behind a car in front of another is to have an effect with the 2 lines above, normally a 1.5x car's width.
You want to increase dirty air. You can approach this in different ways. You can lower the lift and / or increase the drag value. I would start with lowering the lift, because it does not affect handling. You have to change these values for every team, common and common.fom.
Good luck!