With the engine off, loosen the knurled nuts and remove the reservoir cap.
The fluid level should be between the marks on the dipstick.
Top up with Pentosin CHF 7.1 or, if not available, LFIM if necessary. The liquid level should not reach the upper mark on the dipstick a little.
Close the reservoir lid, tighten the knurled nut. Make sure the lid is tightly closed.