Hello Team,
Here is how you get the first and the second line of your email body.
Step 1 - Initialize a variable, enter the Type as STRING.
Do not forget to hit an ENTER in the Value of the Intialize a variable action.
Basically just go the Value field of the action "Initialize Variable" and hit an enter once in the body area.

Step 2 - Compose
As shown in the image below, create a COMPOSE action and add Body preview as Inputs.

Step 3 - Compose action with expression
Enter the following expression in COMPOSE action to get the first line of the email.
split(outputs('Compose'),variables('ParseEmail'))[0]

Step 4 - Compose action with expression
Similarly you need to add another compose action to get the second line
split(outputs('Compose'),variables('ParseEmail'))[1]
If there is a space between your first line of the email and the second line then the above expression changes to -
split(outputs('Compose'),variables('ParseEmail'))[2]
Input email-

Outputs-

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