How do I change a user account account expiry to a specific date?

amurleopard

Also see:
chage - change user password expiry information

Change the date to your chosen date.

$ sudo chage -E 2021-12-12 testuser

Verify

$ sudo chage -l testuser
Last password change                                    : Dec 01, 2020
Password expires                                        : Mar 31, 2021
Password inactive                                       : never
Account expires                                         : Dec 12, 2021
Minimum number of days between password change          : 30
Maximum number of days between password change          : 120
Number of days of warning before password expires       : 7