Never used a dlink extender.. but I do have a TP link one.
Much the same, you need to do its initial setup via connecting directly to it.
Usually once you go into its settings via that way.. it SHOULD have an option to find the exisiting wireless in the area... choose it.. enter your key.. and that's it.
GDKitty
Rogers Ignite Xi6, LG 47LV5400 LED TV, Yamaha