I’m a lefty & 3 of my 4 children are lefties, including 2 sons. for my older son,when he was younger, my husband used to blame me saying I handed him things dafka to his left hand. obviously nonsense, but he was worried about tefillin.
since it’s been a long time & I’ve forgotten, I just asked my husband what we did for them to learn how to put on tefillin. my husband said that the Skulener Rebba, shlita, taught my older son; my younger son’s rebbe in yeshiva taught him.
there were no problems, B’H .. don’t worry.