The adjustment is left of the circle. Tighten the nut. Looks like channel lock pliers have been used before….scratches on the nut.

You can ignore it. Or you can shut the water off and repair it.

To repair it would look like this:

1. shut off water on both sides of the filter - prevents the water from draining from the house and making a big mess..

2. loosen the large nut (looks like a compression fitting to me). You don't have to take it all the way apart, just loosen it so you can do step #3,

3. unscrew the brass fitting from the filter base.

4. Apply 3-4 layers of teflon tape on the male threads of the brass fitting.

5. Screw it back into the filter base and tighten it up

6. tighten the large compression nut again

7. open the valves and check for leaks.