How to convert html page to Sharepoint MasterPage On Sharepoint online

Question

  

Hi,

Using Office 365 Sharepoint Online. 

 

I am trying to follow article

"https://www.c-sharpcorner.com/article/create-a-custom-master-page-in-html-for-sharepoint-online/ " to create custom master page on sharepoint online, but as I try to imort files on Sharepoint designer 2013 , it gives me "Acces denied error"

 

 

 

How can I import html file to convert into master Page.

 

Can you help me out this Please.

 

Solution Required : How to create our own Master page in Sharepoint online, as we can create on On Prem by converting out html page to Sharepoint Master Page