how to remove a package install/build by makepkg

Follow this link , I build **Slack** in Arch by makepkg -sri. Unfortunately, it won't start and I decided to remove it. Issue: When I use pacman -Qm slack it returns error: package 'slack' was not found, and pacman -Rns slack surely won't work as well. How can I remove the package and its dependencies? PS which slack cmd returns /usr/bin/slack