The best thing to do is to do physical, on-the-ground outreach. Part of the success of Tinder as well as many other apps before it were that they threw great parties and events on or near college campuses. The promise of free booze, free food, or really free anything will draw a crowd. Start in your own backyard and then recruit "college ambassadors" and pay them a small flat fee to host the parties and provide them a small incentive structure to hit a certain number of registered attendees.

Happy to talk through this with you as I've had some success with college and high school outreach initiatives in the past.

Have you considered identifying groups they are involved in and asking them through that group? There could be a Facebook group for their University or possibly even a Google + Community? Facebook ads can be targeted by many factors, and a university might be one of them. (You'd have to consult an expert on Facebook advertising to find out. I am not one, but I may know others who can tell me.)

Also search LinkedIn for groups related to specific universities. You can often join such groups and interact yourself or you can identify leaders and contact them to ask whether they would be willing to tell the group about your test.

You could also consider advertising in the school paper. Most Universities would have one which you could find by typing in "University paper" in any search engine or by using specific university names in your search, i.e.: "Yale University paper", "USC university paper", etc.

Other ways you could find students are local free classifieds such as Thrifty Nickel, Pennysaver, etc. or by posting on Craigslist.

You could also create something so entertaining it would go viral to reach them (often done in conjunction with Facebook), but that can be a major challenge not easily done without a substantial budget.

Tom Williams has the best idea though - in person outreach in the manner he described will work best. I went ahead and shared these other ideas because I suspect you want to do many campuses and may not have the budget to travel to them all.

Tom has a great idea. However, it is all about marketing. Use every avenue available to get the word out via the internet including Craigslist, blogs, university newspaper ads and articles, etc. first.
Michael T. Irvin
NoHogWashMarketing.com
"It's All About Marketing"
"Get To The Top Without The Slop"
michaelirvin.net

You might also consider a press release through BusinessWire's college and university circuit.

I would like to share with students the best educational resources that can help them improve their grades and successfully graduate from university. I advise everyone to read an interesting article https://www.denver7.com/brand-spotlight/best-college-essay-writing-service-top-8-paper-writing-sites-in-2022 that will definitely be useful to every student. In order to pass the exam, it is extremely important to be able to write an impressive article that will impress the teacher and help you get better grades.