Help-After engine reinstallation one connection left...

Hello freaks,

Thanks to a leak in the cooler, cooling water and automatic oil had united in my A8 to a cappuchino-like mix, which caused damage in the automatic transmission. I was forced to expand the engine and the gearbox. On the engine, timing belts, oil pump, water pump, crankshaftsimmering front and rear and other stuff were replaced. The gearbox was repaired by a specialist company, the converter came new. Now everything is back in the car, ALL plugs are on again (sweat), only one connector is left, I did not take any photos of it during the installation. It is a black hard plastic hose that goes away from the brake booster and has two connections at the back of the engine. One (white) belongs to the throttle valve arch, which goes towards the air filter. The other one with the red text is the one in question in the photo in the appendix, where I have no idea ...

Can you enlighten me?

A thousand thanks in advance and greeting from the mountains

timmie