Mentors can really help hackers make really cool projects at your hackathon. However, it's important to easily connect your hackers to your mentors.
Before the hackathon, you should send them an event pack that explains how mentoring is going to work at the hackathon, so they can get signed up to any platform before the hackathon.
Before hackers arrive, it's best to brief your mentors on the tools they should use to communicate with the hackers, and how to best approach it.
If possible, get your mentors to introduce themselves in your opening ceremony.
Lastly, remember to show appreciation to your mentors!
Slack / Discord Channel
Creating a channel in your hackathons Slack Workspace / Discord Server is the easiest way for hackers to contact mentors. Some hackers, especially new hackers, may feel intimidated to ask for help in a public channel, which defeats the point. Sometimes hackers may private message mentors, but they may only do this if mentors say they can if they don't want to use the channel.
Encourage mentors to put a friendly welcome in the channel so hackers know who to talk to when they want help!
This platform allows you hackers to create tickets, which mentors can pick up and resolve. Downside is it's a bit of a pain to deploy, and everyone has to have an account generated for them.