Give it time. As you can see in your video the fish rubs up against the tentacles and then dives back behind the anemone. By diving back behind the anemone it can't get stung, the tentacles don't reach back there. By slowly rubbing the tentacles, eventually the anemone will recognize the fish as part of itself and won't sting the fish. At that point the fish will dive right into the anemone.
Anemones sting fish. All fish including clownfish. Luckily, clownfish have a slimy mucus covering that protects them from the anemone. However, if this covering is wiped off of a clownfish, it will get stung and possibly be killed by the anemone. In order to live with the anemone clownfish need to protect themselves from nematocyst strikes. Nematocysts are harpoon-like stingers on the anemone’s tentacles used to capture prey and ward off predators. A thick mucus layer helps to protect the clownfish.
The behavior you are seeing is normal behavior. There are a couple of theories on why it is happening.
One theory is that the clownfish rub themselves against the anemone tentacles to smear the anemone's mucus over themselves. This coating tricks the anemone into confusing the fish for itself. Even though clownfish are born with a mucus layer that is already thicker than average, as it grows larger it mixes its mucus with that of the anemone’s to create a stronger barrier. On the off chance the clownfish is stung, it is protected by a thick mucus layer.
The other theory is that the fish produces mucus that contains chemicals (proteins or sugars) that prevent the anemone nematocysts from stinging.
There is evidence for both theories depending on the clownfish species.
VE their little terra cotta clay pot to spawn in.