Reading between the lines, it would seem there is "bad blood" between your client (A) and a previous developer (B)? In which B controls the previous channel and will not surrender the name - but A claims rights over it? Does not sound like something the Co will be interested in being involved as arbiter but let's see.
If things are really bad, i assume your client can submit a DMCA copyright claim - but be ready with proof and if the other side answers with a DMCA counter-claim, A should escalate with a lawsuit against B - or RokuCo cannot keep a channel down on mere claims (legally anyway).
If B is cooperative though, name switch should be easy - or B can even arrange all old installs to switch to the new app.