Depends on how it was installed. Sometimes there’s a pair of little valves under the tap, one for hot and one for cold. If there isn’t then it’s usually inside the tap, accessed by popping off the cover cap that’s on the front of the lever.
If you’ve got the manufacturer and model name you should be able to find the installation instructions on line, which will show you how to make adjustments or replace parts as necessary.
These days taps don’t have washers so they shouldn’t get progressively ‘softer’ and start to leak as their age.