“keeps freezing” / “It froze while I was writing a really long message.”
Freeze means to turn to ice, but it is also used when a computer or app stops responding. Keep ...ing means to do something repeatedly, and the past tense is froze. Here the email app keeps freezing, so Tina cannot send anything. Line 3 means "It froze while I was in the middle of writing a really long message."
“upload a screenshot of the frozen app to our support page”
A screenshot is an image saved from the screen, and upload ... to ... means to send a file to a website. The agent asks Tina to capture an image of the frozen app and send it through the support web page, not to report an error code. She does not need the broken email app to send it.
“Your love life isn't covered by tech support.”
Love life means one's romantic life, and be covered by ... means to be included in what something handles. When Tina even asks for help getting a reply from the guy she likes, the agent separates fixing the app from relationship advice. The punchline applies the language of insurance or warranty coverage to romance: "Your love life is not covered."