As GM how access D&D Monster Manual

Hi, It's been a long time since I used Roll20. I purchased the D&D 5E PHB and Monster Manual. I have created a game and I purchased the Sunless Citadel adventure and I added it to the game as an "Add on."  So far, so good. I want to add an overland map and some encounter maps to flesh out the game. When I access the journal, the only monster entries I see (and  can find) are the monsters in the adventure.  What do I need to do to access the Monster Manual?

Go to the setting page (outside the game) and make sure you are using a character sheet that supports compendiums such as the official 5e sheet. Choose the Compendium settings also on that page and choose what compendium you wish to have access in that game. Save the settings then when you go into the game you should have an additional tab called Compendium (looks like an i with a blue background). That should be your access to the Monster manual and PHB.

That worked. THANK YOU!!

Good luck and have fun.

Oh, just a heads up. I'm not positive, as I don't play 5e or use the compendiums, but your players might have access to the compendiums also. You can re-enter the game as a player and double check if a player can or not  I would recommend creating a dummy account and using it to check everything from a player's perspective. If you are using chrome, use firefox with the dummy account. This will let you have the dummy account and your GM account in the game at the same time without to much crossover.

If the Monster Manual is in the game, players will have access to it. If this forms a trust or metagame issue, you can do your prep work with the MM turned on in the compendium, and run the session with it turned off. Individual compendiums sources can be toggled on the game's settings page. In reality though, the monster statblocks and info are available in so many ways (D&D Beyond, print books, SRD sites and so forth) that there's probably little point in making the effort.