This is fixed with the recent version releases. 
I have custom certificate version 3.8.6 (2019111807) installed on Moodle 3.8.2+ (Build: 20200320) but am getting a blank page when I tried to view the certificate. It looks fine in the templates setting
Did you load the template in that custom certificate activity? See https://docs.moodle.org/311/en/Custom_certificate_module.
Cannot see the Edit custom certificate cog wheel. I can only get to Edit setting for the resource on the page
Yes I did but cannot see the option to edit These are the permissions
I cannot find the edit custom certificate settings to load template I've made
It's OK I've found the edit settings now to load the certificate template
