I have never used a separate yeast strain to bottle. I always used the yeast that remains when I rack from fermenter to bottling bucket. What are you trying to accomplish?
I know that some commercial breweries use a separatre yeast to bottle, to protect their fermentation strain. They filter out the fermenting yeast and use something different for bottling.
I know some brewers inoculate with a separate yeast if the brew has been in the fermenter for a prolonged period of time (a year) and they fear the yeast may be dead.
I know some brewers use a separate strain on a really big beer if the fermenting strain does not have the alcohol tolerance to operate in the bottle.
Assuming one of these situations applies to you, the process should be fairly straightforward. Prepare a starter, let it ferment out, add the appropriate bottling solution to the bucket, add the yeast, rack over top of it and bottle as usual.
Be careful if you choose to add champagne yeast. It has a high alcohol tolerance. Take precautions against bottle bombs.