A white coating on your tongue means that you have oral thrush which is a fungus infection on your tongue caused by bacteria.
I've had oral thrush on my tongue and eventually it went away within a few weeks.
I would recommend gargling with some hydrogen peroxide or some apple cider vinegar to help kill the bacteria on your tongue.
Brushing your tongue using some apple cider vinegar and hydrogen peroxide can also help kill the bacteria on your tongue when you have oral thrush or the fungal infection on your tongue.
The white tongue is not usually anything serious and eventually goes away and is commonly caused by debris, bacteria and dead cells getting lodged between the enlarged and sometimes inflamed papillae.