You could syphon out the coolant/washer fluid mix with a hose & 1/4 fill Resivoir with a mix of water & Mr.Clean. Disconnect hose from wiper sprays or Washer Motor & pump the cleaner out. The 1/4 fill with Washer Fluid & empty out again.
Or remove Resivoir:
Easiest way is to insert one end of a long piece of hose into the Resivoir, until it reaches bottom.Insert the other end of the hose into a container on the ground (lower then the resivoir)
Next, take a short piece of hose, insert one end into the Resivoir & wrap it & the other hose with a rag that will cover the Resivoir hole. Blow into the other end of the short piece of hose, while holding rag to seal the hole & hoses.The pressure of the air will force the Coolant/washer fluid out the long hose & into the cantainer. Once the fluid starts coming out, stop blowing & let it syphon out.Just be sure not to move the Long hose