The term you are looking for is Kathenotheism. It was coined by Max Muller from Greek kath' hen "one by one" i.e. kata- "according to" + en- "one" plus -theism.
So, in Kathenotheism (it is not a religion in itself, it is use to denote a particular type of religion) you worship one God head at a time and then move ahead to worship another Gods (Trinity)/Deities in same sect, or religion.
Reference from Wikipedia https://en.wikipedia.org/wiki/Kathenotheism
Müller coined the term in reference to the Vedas, where he explained each deity is treated as supreme in turn.
Please note, Kathenotheism is different from Polytheism. In Polytheism, we worship all Gods (Trinity) and other deities at the same time, but in Kathenotheism we worship ONLY one God at a time, then move ahead to worship another one.
Also, note that Kathenotheism is different from Henotheism. Henotheist person, worships only one God, and neglects all other. Henotheist, does know, that there exists other Gods and Deities, but she/he worships only ONE God. The word Henotheism was also coined by Max Muller.
I don't want to complicate things for you, but I think you should also know, the difference between Monotheism and Henotheism. Monotheism is different from Henotheism, in a way, that in Monotheism you know that there is only one God and no other i.e. no concept of Trinity or deities.