Actions to undertake as an Admin after changing the permission mode

Dear Project Server users,

I have posted a question earlier about implications of switching to Project Server permission mode from SharePoint permission mode. You can see some of the implications on this link (thanks to Guillaume :D): (https://social.technet.microsoft.com/Forums/projectserver/en-US/92f0e75d-996b-4391-8198-7950c5552e08/implications-of-switching-to-project-server-permission-mode-from-sharepoint-permission-mode?forum=projserv2010setup)

We have Project Server on premises. So, not Project Online. The last time we tried to switch permission mode to Project Server permission mode the admin could not gain access to the server, and hence, give access to other users.

I have seen some posts on this forum, such as this one: (https://social.technet.microsoft.com/Forums/en-US/b199ea8c-0d67-4678-b21d-2a0bb873d427/when-we-are-changing-the-permission-mode-from-sharepoint-to-project-server-mode-not-able-to-set?forum=projectonline) but don't think that they describe in enough detail the actions to undertake, as admin, to gain access to Project Server 2013 after the change. I have also seen posts explaining how you should just type -AdministratorAccount code to your permission changing code and that that will give you access.

Can anybody who has had experience with this describe what should an admin do to have access when changing the mode from SharePoint to Project Server?

Sorry for the long text,

Any help is welcome,

Sincerely,
Petar