HELP! - Login page gone when I transferred app to new team

At the moment, the app still shows the Airtable tables but I will never be able to add new ones.
I used to have a sign in page that doesn’t seem to work anymore. When the correct username and password are entered, it should redirect and open up the first tab of information from one of my tables. Instead, nothing happens.
The sign in page was used to control the visibility of other pages.
Once signed in, I used to have icons at the bottom of the screen in the nav bar for each page. They have gone.
The whole thing is a mess and I don’t know what to do to fix it. I worked on it all weekend, with no success.