Static Mixers are designed to reduce Detector Noise associated with heterogeneity of multiple mixed Solvent sources by mixing more thoroughly than can be accomplished with a proportioning valve in the HPLC Instrument.

The best place for the Static Mixer is after the solvents have been mixed by the Instrument but before the Sample has been Injected.

You would simply remove the tubing from the pump assemblage outlet and insert the static mixer between these two components.