combining titles in a series

after finally learning how to get books placed into a series - I placed a bunch into various series. as an example I placed several items into various "series" of rod & staff publications. when options appeared, I clicked on each title. many of these titles are the same work. how do we reduce the number of titles to its core entries?

thank u

You're probably going to have to explain which series, which specific work/s.
Your post reads as though there are works that need combined.

Publisher series can't be combined with a regular series. One would need to be emptied and deleted, if it isn't supposed to exist.