I heard there's a swimming test, but I can't swim, what can I do?

Don’t worry, you’ll get taught how to swim in the Army.

Hi, the test isn’t about style or speed it’s just about keeping your head above water and it’s really just to ensure you are safe. If you can’t swim the Army will help you learn. I’m not a great swimmer and I passed the test easily.

You will have plenty of lessons and practice beforehand. The test is designed to ensure you can safely swim if required.
The test is as follows -
Enter the pool in a step in manner
Tread water for 2 minutes
Swim 100 meters in a front facing stroke without touching the sides or bottom
Exit the pool

It's okay, you will be taught in the army. I also couldn't swim when I joined however I was taken through progressive training to pass the test.