how to manually remove MSI installation?

If this is a proper small update / minor upgrade .msi file to fix an earlier version which couldn't uninstall, just install it with msiexec /i updated.msi REINSTALLMODE=vomus (and maybe also REINSTALL=ALL). The v of vomus will have Windows Installer replace the old package with the new, and then you can uninstall normally.

But of course all this is unnecessary these days with the ability to test on a virtual machine you can just revert...

Remove your install entry in registry here. You might need to find out the GUID from your setup project.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall OR
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall

Check also DisplayName, it can be helpful when your product has defined friendly name.