Updated to ubuntu 18.04 LTS from 16.04 LTS, lost UART1

I’ve updated my Beaglebone Black to Ubuntu 18.04. Now my UART1 is not working. In dmsg, I get

[    4.437857] bone_capemgr bone_capemgr: slot #4: No compatible property for 'BB-UART1'
[    4.445921] bone_capemgr bone_capemgr: slot #4: Failed verification
[    4.453875] bone_capemgr bone_capemgr: loader: failed to load slot-4 BB-UART1:00A0 (prio 0)

I’m running kernel 4.4.80-ti-r116. I think I should update to 4.19(?), but when I do `sudo /opt/scripts/tools/update_kernel.sh --ti-channel --lts-4_19’ I get the error

E: Unable to locate package seeed-modules-4.19.94-ti-r73
E: Couldn't find any package by glob 'seeed-modules-4.19.94-ti-r73'
E: Couldn't find any package by regex 'seeed-modules-4.19.94-ti-r73'

Research tells me I should sudo apt install bbb.io-kernel-4.19-ti-rt-am335x, but I get Unable to locate package bbb.io-kernel-4.19-ti-rt-am335x

I just want mu UART1 back… What do I need to do?

Thanks in advance.