1. download the latest Plesk extension from here

2. edit file /usr/local/psa/admin/conf/panel.ini , create it if not exists.

3. add following content:

[ext-catalog]
extensionUpload = true

4. save the change , now navigate to **Plesk extension** ---> **my extension** , as screenshot , you will see an ** upload** button, and upload the package downloaded in step 1