On a Windows 10 machine, the licence.xml file is located here (for each module):
Affinity Photo:
C:\ProgramData\Affinity\Photo\1.0\licence.xml
Affinity Publisher:
C:\ProgramData\Affinity\Publisher\1.0\licence.xml
Affinity Designer:
C:\ProgramData\Affinity\Designer\1.0\licence.xml
Notes:
You can either delete that file or edit it
If you chose to edit the file and replace the old key/email with the new key/email, don’t forget to remove the hyphen (or dash) in the registration key that you copied from the Affinity Store
If you deleted the file, the next time you run the software, it will ask you to enter your email and the reg. key
If you edited the file, the next time you run the software, it will not ask your for anything. It will recognize the license and everything will work as normal