Follow these few steps in order to open a mySongBook tab in Guitar Pro 7.5.
From Guitar Pro 7.5:
Open Guitar Pro 7.5 and select Browse from the Welcome page.
Fill in both your email address and password.
Access your mySongBook purchases directly from this window, select one of them to open it in Guitar Pro 7.5.
Note that you can access the Free Tab of the Day from this window or even manage your tabs and access the mySongBook website.
From the mySongBook website:
Connect to your mySongBook account from the mySongBook website.
Select the tab that you want to open from the mySongBook website.
Select "open it : open tabs with Guitar Pro 7"
The following alert pops up : "Do you want to allow this page to open “Guitar Pro 7?"
Your tab is now opened in Guitar Pro 7.5.
These steps applies for mySongBook subscribers. Please note that you will have to either purchase the tab or purchase a mySongBook subscription prior to access your score.
Note that you can access the tabs you previously purchased from the "My Tabs" menu located from the right corner below your User name.