postgres user password reset problem

I know this is a common problem because the web is full of advice. Sadly
none of it has worked for me.

I re-installed PostgreSQL 10 on Ubuntu 18.04 after removing it with
--purge and now I can't get back into it.

I have assigned a Linux password to the postgres user and I can sudo or
su but psql is demanding its own password for its postgres user. The log
says ...

2020-06-12 14:03:00.019 AEST [22214] postgres(at)postgres FATAL: password
authentication failed for user "postgres" 2020-06-12 14:03:00.019 AEST
[22214] postgres(at)postgres DETAIL: User "postgres" has no password
assigned. Connection matched pg_hba.conf line 92: "host all all
127.0.0.1/32 md5"

No password assigned. Which I knew. So I removed that "host all"  line
from pg_hba leaving only the "local all" lines and failed again ... the
log now says ...

2020-06-12 14:09:12.846 AEST [22462] LOG: database system is ready to
accept connections 2020-06-12 14:09:13.440 AEST [22470]
[unknown](at)[unknown] LOG: incomplete startup packet 2020-06-12
14:09:59.424 AEST [22498] postgres(at)postgres FATAL: no pg_hba.conf entry
for host "127.0.0.1", user "postgres", database "postgres", SSL on
2020-06-12 14:09:59.427 AEST [22499] postgres(at)postgres FATAL: no
pg_hba.conf entry for host "127.0.0.1", user "postgres", database
"postgres", SSL off

I am fairly lost here. My objective is to get the postgres user
re-established, get my own user re-established, re-load the dump files
and get back into production.

Any advice appreciated

Thanks

Mike