First make sure you review page 5 in the user guide:
https://pae-web.presonusmusic.com/downloads/products/pdf/Quantum_2626_Owners_Manual_EN_04052020.pdf
You're going to connect the preamp outputs of channels 1 and 2 out from the 2626 to your compressor inputs 1 and 2.
Then plug cables from outputs 1 and 2 of that device and plug them into returns 1 and 2 on quantum.