I first placed myself in the raspberry pi$4$ card with the ssh command ubuntu@$192\mathrm{.}168\mathrm{.}28\mathrm{.}24.$ After that, I now encounter problems when I type the command sudo systemctl disable hciuart in my Linux terminal which gives me the error failed to desable unit: unit fil hciuart.service does not exist. I cannot correct this error which will allow me to correct the problem with the default controller. I am on ubuntu $20\mathrm{.}04.$ Can you help me please?