In “She changed the password”, When did she change it? If in the past tense, you say “She has changed the password” or “She had changed the password”.

When you retelling a story about your past, you usually say “I saw a lion”.

There are lots of Present Perfect tenses, e.g. Present Perfect simple or Present Perfect progressive. Can you be a bit more specific?

Hopes this helps! Good luck!

I had seen a lion…

Present Perfect: has/have plus verb

Past Perfect: had plus verb

Had done something means you did it, it’s over.

Have done something means you did it, but it still continues into the present.

Hope this helps