How can I get rid of mildew/ mold on my floor in my wash room, it is t

There is too much moisture in your bathroom. If you do not have an exhaust fan, one needs to be installed. To clean the floor of mildew I'd use bleach water. If that doesn't work, I'd scrub with a cleanser that has bleach in it. Maybe make a paste of it and leave it for an hour or so before rinsing.

tea tree oil. It gets rid of it and it doesn't come back.

I would make sure the room has good air flow after you get rid of it.

I agree with Sal85902, a ceiling exhaust fan may be necessary to keep it from being a persistent problem. I use vinegar with baking soda. There is also another product called Damp arid. You place a small plastic bucket filled with crystals that absorb moisture in the air. It turns the crystals into water. When full, empty and refill with the crystals.

https://damprid.com/

Tilex

Find a less obvious place and see how deep, how many layer of flooring, the mold affects. You may have to pull it All out. Sorry, but this happened here. Four layers of flooring removed, then base layer. We treated the base layer after so ing the leak problem. Difficult smelly work, tedious but totally wothwhile

Find out what kind mold it is because some mold is very hazardous to humans and pets.