Converting the timestamp in Snowflake
Solution 1:
You can cast to a varchar and give, as the second parameter, the format that you want:
SELECT TO_VARCHAR('2021-07-19 02:45:31.000'::Timestamp_TZ, 'yyyy-mm-dd hh:mi:ss')
2021-07-19 02:45:31
(Note I changed the seconds to 31 as there isn't 91 seconds in a minute and also changed your double dash between month and day to a single. I'm assuming those were typos)
Solution 2:
Give you are correct converting the date/timestamp, this is not a convertion problem, it is a presentation problem.
Thus the Date and Time output formatting help is what you need.