I’m a native speaker and I remember struggling with silent letters when writing when I was younger. The best way to learn is to re-read your texts, “relire” as we call it in french. Do it with attention and care, asking yourself questions.
For example you reread this sentence: Il a perdu ses crayons. (He lost his pens.)
Then you ask yourself:
-Qui a perdu ses crayons? Il=masculin= pas de ‘e’ à la fin du verbe. (Who lost their pens? He= masculine= no ‘e’ at the end of verb.)
-Combiens de crayons? Ses crayons= ses est un indicatif au pluriel= crayon avec un ‘s’ à la fin. (How many pens? His pens = french his is the plurial form= ‘s’ at the end of pens.)
It seems super complicated to always do this in the beginning but it will get easier! Plus you can always go back to asking those types of questions if you’re uncertain. I wish you all the best and hope we might cross paths one day!