It's risky adding a larger clown (of the same species) to a tank with only 1 clown. When the first fish was alone, if it was old enough it would have changed into the dominant female. As the new fish was larger, it may also be female. As it appears to be asserting dominance, even if it wasn't already female it will be changing.
They can't change back into males, so that may leave you with 2 females, of which only 1 will survive.
You probably have 2 options
Hope the first fish wasn't already female and things should sort themselves out once dominance has been established.
Return the new larger fish and get one that is smaller. Let your first fish become, or survive, as the dominant female.
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