Load the two sounds you want to sidechain in FL Studio
Route the kick to its own mixer track
Route the target sound to its own mixer track
Select the kick mixer track
Right-click the send arrow to the target mixer track
Choose “Sidechain to this track”
Insert Fruity Limiter on the target mixer track
Open Fruity Limiter and go to the COMP mode
Select the sidechain input in Fruity Limiter
Lower the threshold
Increase the ratio
Adjust attack and release to taste
Play the track and fine-tune the settings
Use volume automation or a volume shaper plugin if preferred