How to load the DLC when it doesn't show in the main screen

First off, i would like to give credit to Panda K for creating the files necessary to get this to work. The page for the files however do not contain an explanation for what to do so here is a tutorial.

To start you will need to download this file from nexusmods
https://www.nexusmods.com/assassinscreedivblackflag/mods/317

After downloading and unzipping, it should contain 2 files, 1.save and ACSaveTool_x64. Next you will need to find your ubisoft save file. It will likely be here, or if you installed it somewhere else you will need to find it. C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegames\[somepersonal-id folder]\437

It is likely in the 437 folder however you may also find it in the 720 folder. Best way to check is to start up the game and see which folder is most recently edited.

You should have 1.save 2.save and 3.save in this folder and in case you have played through the main story previously the larger .save file (around 80 kb size) will contain this. (create a backup just to be safe) You will need the smaller 5.kb folder later that is named either 1.save or 2.save. Depending on what the 5kb file is called rename the 1.save file that you downloaded from nexusmods to that name (so rename it to either 2.save or keep it as 1.save).

You then start up the ACSaveTool_x64.exe and you will be greeted with several options you need to fill in. On "game" select AC4 black flag, "decryption-ID" select detect and it should gray out. "encryption-ID" select the 5 kb save file that is present in the ubisoft folder and you had to find previously. Finally on "save file(s)" open the .save file you downloaded from nexusmods and maybe had to rename.

Press convert and your 1.save that you downloaded from nexusmods should have been edited (check timestamp). Paste this save-file into the save games folder and overwrite the other .save file.

Start up the game and if it worked on the top right you should see that you can start the freedom-cry and aveline dlc.

Hope this tutorial helps.