As Barbara said, most tuners can emit an audible tone.
Also, most give you the option to select a specific note rather than just guess at what note you are trying to tune by giving the closet to what it picks up.
So you can select a note like middle middle C and then tune approximately by ear and then use the tuner to fine tune it.
However don’t be a slave to the tuner for life. The tuner may help you get theoretically perfect or close to it, but perfect isn’t always best sounding. For instance many harpists tune the upper octaves slightly sharp intentionally because it sounds better.
Tuners are great when you are starting out, and are a fantastic tool even for the experienced harpist as they save a lot of time getting in the ballpark, but as you get more experienced your ear will develop and you will start to be able to trust them more. At that point trust your ears even if they don’t match the tuner exactly.