Hi, again! Because of the forced air in convection ovens, they effectively bake as if they are 25F (or so) hotter than a conventional oven. So, if you don't adjust the oven temperature, some things will bake more fully on their outer edges or exposed surfaces before they bake all the way through - just as you experienced. Cookies don't really benefit from being baked in a convection oven, in my opinion, because the forced air also lends to more crusting. Convection ovens are ideal for pie crust, danish, croissants, and other yeasted breads where you want a nice, flaky crust, and where you want a bolt of heat to get them rising. Conversely, they are not so great for cookies and cakes that often benefit from slower, more even baking.
So you have two options: (1) Turn off the forced air (presuming your oven has the ability to turn it on and off; some ovens do and some don't) and bake at your usual temperature, or (2) leave the forced air on and set the oven temperature about 25F lower, and see if this improves the situation.
I hope this helps!
Again, welcome to the site; I hope you enjoy it!