if you have a 3.3V LED and want to solder on the 5V, i would recommend using a resistor of 500 - 700 ohm.
and also resistors are only connected if for example you connect three 3.3V "as a chain" to one 5V point so that it can resist the and ground the electricity going to the LED and borad, but if you have only a 3.3V or 5V LED and want to connect it to the 5V point then there is no need for any resistors to be aplied.
hope this solved something.
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