There is no easy way to make a true X-Y chart in FactoryTalk View ME / PV+.
There's an "X-Y" option in the Trend object that will replace the X-axis with a tag value instead of time, but it still plots points based on time, rather than taking an array of data from array tags and plotting it all at once.
I've seen people create X-Y charts by 'playing' the data out to the Trend object, but it's not an ideal workaround.