I just recently bought ficus benjamina and seated on my apartment corridor which have afternoon sun. Humid enviroment.
i water it 1xperday. leaves started dropping. some leaves turned brown and purplish.
No sign of fungus.
please advise.

watering 1x per day seems like you're overwatering

i was told to water 1x per day
because this problem looks like over or under water.
so am confused.
do i wait until the soul dry then water?

As this is a forum abour bonsai, you may not get the best answers here. It is better to try a forum about houseplants, you will find people there with experience with plants like this.