Hi Mario, since you already have a De Esser built into Studio One Pro it is quite easy to use. It can be found in the compressor vocal presets.
In the sidechain section of the compressor select Int. Sidechain Filter and find the frequency of the s' by clicking the listen button and sweeping the frequency. You can narrow this down and also adjust how much to compress the the frequency when it passes its threshold.
I also have IK De Esser which works great as well as Nectar 3.

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BIAB 2025 Ultrapack- Studio One Pro 7 Windows 11, Mac Mini M4 with Logic Pro 11, Melodyne Studio