Create a 1D array of strings. Wire it to a Transpose 2D Array primitive, or the 2D data input of Write To Spreadsheet File. You've connected a 1D array to a connector looking for a 2D array, so the wire will be broken. Right click on this, and you'll be given the option to Insert Build Array on the RCM. The same works for many scalar-to-array connections, such as when you try wiring a Boolean constant to And Array Elements.
This behaviour's not consistent, however. Try wiring a numeric constant to Sum Array Elements. Ignoring the fact that this is nonsensical, you're not offered the option. Same for connecting a numeric constant to the input of a Mean calculation VI.
The reason I ask is that it's a neat feature I'd use from time to time to make my life easier if I could force its use. For instance, I have a TDMS logging FG which takes a 1D array of clusters of string + variant data. Sometimes I only want to write one property; sometimes I want to write multiple. I'm aware I could make the VI polymorphic if I cared, but having a right click 'Insert Build Array' option every time I forgetfully wire a single cluster to the FG would be fun!