Voodoo Lab

Hello, I'm new to the world of MIDI and have acquired your PX8+.
I'm having a hard time " saving " my program changes.
Let me explain:
the MIDI Out of the PX8+ is connected to the MIDI In (MIDI TRS cable) of my Wampler Terraform and the Thru output of my Wampler Terraform (MIDI TRS cable) is connected to the MIDI In of my Source Audio Collider.
First problem: when the 2 pedals are connected in this way, changing presets on the Voodoo Lab PX8 will only cause presets to be changed on the Collider and not on the 2 pedals simultaneously...
Second problem: but how to save program changes from the PX8+ to a MIDI device? This is not explained at all in the manual.
For example: I would like my Preset BANK 1 Preset A on the PX8+ to correspond to a preset change on Terraform on what is stored for example in preset 4. How do I do this? I have succeeded a few times but always by chance. (All my devices are on Channel 1)
Thank you for your lights.
David