Inadvertently cashed a SEP-IRA distribution check made out to my Custodial SEP-IRA account. Was issued a 1099-B, but should have been issued a 1099-R

After transferring all whole shares from my Equiniti SEP-IRA custodial account to another SEP-IRA custodial of mine at Etrade, I was issued and inadvertently cashed a residual dividend payment from Equiniti (which was made out to my name, but with the custodian designation as well), which reflceted a dividend payment that occurred after the share transfer date.  Equiniti then issued me a 1099-B, when it should have issued a 1099-R to me reflecting an IRA distribution. But Equiniti says it cannot/does not issued 1099-R forms.  How do I fix or explain the erroneous form to the IRS?