Turning Harissa into Hot Sauce
The only difference between something that would be called "hot sauce" and a "chili paste" is the consistency, and perhaps how finely ground the chilis are (though harissas are usually pretty finely ground.) They can both be used to cook with, and they can both be used as condiments. 

If there's a specific type of hot sauce you're looking to replicate (e.g. Tobasco,) you're probably going to fail. Despite the fact that there seems to be more in common than differences among hot sauces, there's a tremendous amount of variation in how they're made, and the processes tend to be counter-intuitively complex. What peppers? Fermented or fresh? Cooked or raw? Vinegar, oil, or another base? Is there an added thickener? How hot? Is it sweet? What's the salt content? 

For example, my favorite hot sauce, Azorean Piri Piri sauce, is made by keeping salted peppers between two wooden crates while they drain and ferment. Nando's famous piri piri marinade (which could certainly be considered a hot sauce) is completely different, using cooked, pureed peppers. If I had some sort of piri piri chili paste, it would not be suitable to make either of these sauces.

However, If you're looking to make any sort of hot sauce at all, I'd highly recommend experimenting with small amounts. You might just need to loosen it up with some vinegar and/or water, and salt. Maybe add a touch of sugar to round it out. Maybe puree some garlic. Maybe add some smoked paprika for more depth. Keep in mind that it will probably be a bit harsh when you're tasting it directly (you may want to get a box of bland crackers to use,) but whatever you're putting it on will almost certainly drastically mute the hot/sharp/pungent notes significantly.

Good luck!