Hello from Lake County.  Thank you for letting me help answer your problem.  I have actually had the same thing happen to me.  Lily of the Valley is one of my favorite flowers.  Years ago I planted some in the bed with my Hydrangeas thinking that they would bloom before them.  For many years, they were able to coexist quite nicely, but 20 years fast forward, they have almost entirely choked out the hydrangeas.  If you are good with that, then just leave them.  If not, here are 2 articles on controlling Lily of the Valley, and one on Hydrangea care.  You can smother the LOTV, pull them up or use chemical control.  with the latter you need to be very careful and remember that the label is the law and to watch overspray.

https://www.gardeningknowhow.com/ornamental/bulbs/lily-of-the-valley/lily-of-the-valley-control.htm

https://homeguides.sfgate.com/kill-lily-valley-41593.html

https://extension.oregonstate.edu/gardening/flowers-shrubs-trees/general-care-hydrangeas

Hope this helps!

Shelley