Simple solution, this process takes no more than 15 min... get a small bucket put the anemone and the clownfish in. Make sure you corner them together with no space so the fish have no place to go beside getting close to the anemone. The clownfish will slowly settle to the anemone get stung during the process. In about 10-15 min you will see the fish moves all over the anemone. Black spot is on the fish from the anemone sting if the the fish is tank raise , wild caught there are no spot on them. After that put them in your main tank, the fish will dive right in once you release them.
Why suggest this? It will happen when it happens, if it happens at all. Why force the issue and potentially force the fish to get stung?
I've had clownfish in the past the never went near a nem, others took to them immediately, and still others took months to host.
I had a pair once where one clown started hosting and the other wanted nothing to do with it. Over a period of weeks the hosting clown kept darting to the other clown and back to the nem, kinda like it was saying "come on in!". After 2-3 weeks both clowns were hosting.
Just let them host at their own speed.
Some people doesn't like to wait for the process to happen.
Those are the type of people that should re-think their involvement in the hobby.
Any one researching saltwater reefing for even a short period of time should get the message that "nothing happens fast" in this hobby.