You will probably have a bunch of unused dependencies (orphans), so you can list those with
pacman -Qdtq
and remove them manually (exactly as above). Or you can use a pacman wrapper/AUR helper, like yay and run the following command to remove all of these orphans at once:
Looks like you assumed pacseek is preinstalled. In most Arch distros it is not. As for remove of those files follow the instructions in Kresimir’s post.
Invest some time in reading up on package management and system maintenance on Arch.
Here below there are a couple of links to start with.
If you find the information overwhelming at first, take it in by bits and pieces. The reward is all the more great in the long run compared to the time invested.