IEM n00b needs help

I just got a pair of JVC Marshmallows. They’re my first IEMs, so I don’t know if my experience is normal or not.

I get a good seal at first and thus good sound, but only for a while. They gradually work their way further out of my ear canal and eventually, everything sounds like mall music. Then I have to take them out and re-insert, and repeat several times over the course of a workday.

Would new tips fix this? Is this a sign that my ears just aren’t made for IEMs? Or, is this just how IEMs are? I have no idea what to do.