In most cases, you don’t have to do anything.
With 1Blocker Premium, filters are updated in the background several times per week, and the app also refreshes them every time you launch it.
In the free version, the latest filters are included with every 1Blocker app update available on the App Store, so keeping the app up to date is enough.
You can check which filter version you currently have at the bottom of the app’s main screen.
If background updates don’t seem to be running, the setup steps are here: Filter updates in 1Blocker