I would re-center the mast and forget about the yard's tuning. Loosen the forestay and tighten the aft stay. Of course the shrouds and lowers will have to be loosened up too.  Focus on forward and aft centering first before you do side to side. Then once the mast is centered,  tune it. 

The furling drum will have to be removed in order to slide the foil  up the forestay to allow access to the turnbuckle. Hold the foil  in place/lift via a well wrapped/tied jib halyard. Do an internet search for your brand of furler and there should be a YouTube video on how to access the forestay turnbuckle. Key tip- tie the two halves of the furling drum together and secure with a line to the pulpit or bow cleat before you separate the drum from the foil. This will prevent accidentally dropping them overboard which is very easy to do. It's best to do this work with the bow close in to the dock, otherwise you'll have to use some contorted positions while laying on the foredeck. Work slowly so you don't drop screws overboard and use an anti-seize lubricant when reinstalling. 

When you're done with the initial tune, lower the foil back in place slowly or you risk telescoping parts together with an interference fit and it will be a pain to separate things. (especially true if you have Schaefer Furling).