The 99Plugs Update Manager is a product like any other, which means it gets updates like any other. Whether you have to do anything about that depends on what you bought.
If you have a VIP Access Pass
Nothing to do. Your pass covers the whole library and the Update Manager is part of it. One pass entry keeps everything updating, the Update Manager included.
If you bought items individually
Add it. The Update Manager has its own item name and update key, and if you never enter them, it never updates itself.
This is the step individual buyers miss most often.
- Open your account dashboard on 99plugs.com and go to the Update Keys section.
- Find the 99Plugs Update Manager entry.
- In WordPress, go to Tools → 99Plugs and add the item name and update key the same way you added everything else.
Why it is worth two minutes
The Update Manager is the piece that delivers everything else. When it goes stale, the symptoms do not look like a stale updater. They look like updates that quietly stop arriving, and that sends people hunting through their plugin list instead of the one plugin actually responsible.
Full setup procedure: How to enable auto updates.