1. You can control effects with external MIDI device alongside the mixer.
You may need to assign MIDI.
Here is a manual for MIDI-LEARN-FUNCTION.
https://rekordbox.com/_app/files/img/MIDI_LEARN_operation_guide_en.pdf
2. You can change "FX BPM" with tap button on the GUI (similar to Beat Effect of DJM)
・Click "BPM LABEL"

・Change to TAP MODE

I hope I can be of any help to you.