Thats pretty easy.

Put the bike on the paddock stand. At the rear of the swinging arm there is a large pinch bolt (has a 17mm head i think) slacken that, then using the the tool you have turn the eccentric hub clockwise or anti clockwise to tighten or loosen the chain.

The tool slots into the eccentric hub just behind the sprocket. Pull the handle of the tool up to tighten and down to loosen.

Once you have the chain about right retighten the pinch bolt and recheck the chain (they tend to tighten up as you tighten the pinch bolt)

I cant remember the torque for the pinch bolt as i think the RC45 is differnt to yours. About 25mm of slack seems right as long as you dont have any of the HRC chain roller kits.

I hope all that makes sence