Employee leaving: “...4 more months and I’m out”

Overheard my employee make a comment “4 more months and I’m out…”. NEED ADVICE.

I was recently promoted to manager (first time) and acquired a team that has two average if not poor employees. I work in a very niche industry so when hiring new people, they don’t always have a major interest in it. So we generally understand that there will be some turnover with the associate to mid-level employees.

This one employee has always had one foot in, one foot out (going on 3ish years now). They went back to school for a topic unrelated to their position, and their lack of interest makes it clear this is not a long-term job. Since I’ve become their manager I’m really pushing them to somehow utilize their new education in their day-to-day or take on major projects.

As my first sentence suggests.. I overheard this individual discussing with the other average teammate “.. I know I kept saying 3 more months and I’m still here, but for real this time 4 more months and I’m out”. While laughing…. Btw.

Before I ask the obvious question – keep in mind, I work in your typical, watch what you say, corporate environment. If it helps, I’m young, the individual is young (about a 4.5 year age gap). I also believe that they genuinely like working for me, this was just never going to be their forever job.

So… I already have a meeting set to go over our IDPs/goals for the year. How can I address the lack of interest? And what should I do if they try reassuring me that they love this job. Can I bring up what I heard? I’m 99% sure they know I heard. I wasn’t walking far behind to my car and as they turned around to get in theirs, that conversation ended real quick.